Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

https://hal.archives-ouvertes.fr/hal-00886451/document

Plant drought stress: effects, mechanisms and management

Abiotic stresses are one of the major constraints to crop production and food security worldwide. The situation has aggravated due to the drastic and rapid changes in global climate. Heat and drought stress are undoubtedly the two most important stresses having huge impact on growth and productivity of the crops. It is very important to understand the physiological, biochemical and ecological interventions related to these stresses for better management. A wide range of plant responses to these stresses could be generalized into morphological, physiological and biochemical responses. Interestingly, this review provides a detailed account of plant responses to heat and drought stresses with special focus on highlighting the commonalities and differences. Crop growth and yields are negatively affected by sub-optimal water supply and abnormal temperatures due to physical damages, physiological disruptions and biochemical changes. Both these stresses have multi-lateral impacts and therefore, complex in mechanistic action. A better understanding of plant responses to these stresses has pragmatic implication for remedies and management. A comprehensive account of conventional as well as modern approaches to deal with heat and drought stresses have also been presented here. A side-by-side critical discussion on salient responses and management strategies for these two important abiotic stresses provides a unique insight into the phenomena. A holistic approach taking into account the different management options to deal with heat and drought stress simultaneously could be a win-win approach in future.

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Crop Production under Drought and Heat Stress: Plant Responses and Management Options

Plants face a combination of different abiotic stresses under field conditions which are lethal to plant growth and production. Simultaneous occurrence of chilling and drought stresses in plants due to the drastic and rapid global climate changes, can alter the morphological, physiological and molecular responses. Both these stresses adversely affect the plant growth and yields due to physical damages, physiological and biochemical disruptions, and molecular changes. In general, the co-occurrence of chilling and drought combination is even worse for crop production rather than an individual stress condition. Plants attain various common and different physiological and molecular protective approaches for tolerance under chilling and drought stresses. Nevertheless, plant responses to a combination of chilling and drought stresses are unique from those to individual stress. In the present review, we summarized the recent evidence on plant responses to chilling and drought stresses on shared as well as unique basis and tried to find a common thread potentially underlying these responses. We addressed the possible cross talk between plant responses to these stresses and discussed the potential management strategies for regulating the mechanisms of plant tolerance to drought and/or chilling stresses. To date, various novel approaches have been tested in minimizing the negative effects of combine stresses. Despite of the main improvements there is still a big room for improvement in combination of drought and chilling tolerance. Thus, future researches particularly using biotechnological and molecular approaches should be carried out to develop genetically engineered plants with enhanced tolerance against these stress factors.

/pdf/chilling-and-drought-stresses-in-crop-plants-implications-3zvxfs5ueg.pdf

Chilling and Drought Stresses in Crop Plants: Implications, Cross Talk, and Potential Management Opportunities

Plants are exposed to any number of potentially adverse environmental conditions such as water deficit, high salinity, extreme temperature, submergence, etc. These abiotic stresses adversely affect the plant growth and productivity. Nowadays various strategies are employed to generate plants that can withstand these stresses. In recent years, seed priming has been developed as an indispensable method to produce tolerant plants against various stresses. Seed priming is the induction of a particular physiological state in plants by the treatment of natural and synthetic compounds to the seeds before germination. In plant defense, priming is defined as a physiological process by which a plant prepares to respond to imminent abiotic stress more quickly or aggressively. Moreover, plants raised from primed seeds showed sturdy and quick cellular defense response against abiotic stresses. Priming for enhanced resistance to abiotic stress obviously is operating via various pathways involved in different metabolic processes. The seedlings emerging from primed seeds showed early and uniform germination. Moreover, the overall growth of plants is enhanced due to the seed-priming treatments. The main objective of this review is to provide an overview of various crops in which seed priming is practiced and about various seed-priming methods and its effects.

Seed priming for abiotic stress tolerance: an overview

A new perspective of phytohormones in salinity tolerance: Regulation of proline metabolism

Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.)

This research was carried out to determine the effects of irrigation applied at different growth stages on yield, yield components and oil content of sunflower during 2002 and 2003. Sunflower cultivars Sanbro, Tarsan-1018 and Ozdemirbey were used as materials in the experiment which was designed in a split plot of randomized complete blocks with three replications. Seven irrigation schedules; I 0 = nonirrigated (control), I 1 = irrigation at vegetative stage, I 2 = irrigation at heading stage, I 3 = irrigation at flowering stage, I 4 = I 1 + I 3 (two irrigations) I 5 = I 1 + I 2 + I 3 (three irrigations) and I 6 = I 1 + I 2 + I 3 + irrigation at milking stage were applied. According to the results of the research, plant height and head diameter by cultivars and irrigations ranged between 106 to 183 cm and 12.5 to 19.3 cm, respectively. Irrigations at all growth stages increased seed yield by 43.1% in 2002 and 77.2% in 2003. The results revealed that three irrigations should be scheduled at vegetative, bud formation and flowering stages. Under severe conditions of water scarcity, it would be better if irrigation is applied at flowering stage. Key words: Sunflower, irrigation, yield, oil ratio.

/pdf/seed-yield-and-oil-content-of-some-sunflower-helianthus-55zdb4f46h.pdf

Seed yield and oil content of some sunflower (Helianthus annuus L.) hybrids irrigated at different growth stages

Effects of different row distances and various nitrogen doses on the yield components of a safflower variety.

Oz: Bu calisma 2007 yilinda bazi cerezlik aycicegi cesit ve genotiplerinin cimlenmesi uzerine NaCl konsantrasyonlarinin etkilerini belirlemek amaciyla yurutulmustur. Arastirmada materyal olarak Opal, Beyaz, Suriye Nevadasi, Elazig, Kibris, 01M007, 01M008, 01M012 ve 01M013 aycicegi genotipleri ve 5, 10 ve 20 dS/m NaCl konsantrasyonlari ile kontrol olarak distile su (0 dS/m) kullanilmistir. Ekimden itibaren 10. gunde cimlenme yuzdesi (%), ortalama cimlenme zamani (gun), kok uzunlugu (cm), fide uzunlugu (cm), fide yas agirligi (mg) ve fide kuru agirligi (mg) olcumleri yapilmistir. Arastirma sonucunda, genotiplerin NaCl konsantrasyonlarina farkli tepkiler gosterdigi belirlenmistir. Artan NaCl seviyeleri cimlenme yuzdesinin azalmasina, ortalama cimlenme zamaninin uzamasina ve fide gelisiminin engellenmesine neden olmustur. Beyaz genotipi tohumlari, NaCl konsantrasyonlarindan en az etkilenen genotip olmustur. 10 dS/m NaCl cimlenme ve fide gelisimini engellemistir. Cimlenmelerine ragmen bes genotipte fide gelisimi belirlenmedigi icin NaCl'nin fide gelisimini cimlenmeden daha fazla olumsuz sekilde etkiledigi soylenebilir. Ayrica tohumlarin kabuk oraninin, tuz konsantrasyonlarina bakilmaksizin, su alimi ve cimlenmede onemli bir etken oldugu sonucuna varilmistir. Kabuk oraniyla su alimi arasindaki olumlu ve onemli korelasyon (r=0.692**) bunun bir gostergesi olarak degerlendirilmistir. Abstract: This study was conducted to investigate the effects of NaCl levels on germination of confectionary sunflower genotypes in 2007. Seeds of Opal, Beyaz, Suriye Nevadasi, Elazig, Kibris, 01M007, 01M008, 01M012 and 01M013 were used as material. Electrical conductivity (EC) values of NaCl solutions were 5, 10 and 20 dS/m. Distilled water (0 dS/m) served as control. Germination percentage (%), mean germination time (day), root length (cm), shoot length (cm), seedling fresh and dry weight (mg) were measured at 10 days after sowing. As a result of the research, genotypes showed different response to NaCl. Increased NaCl levels resulted in both decreasing in germination and inhibiting of seedling growth but increasing in mean germination time. The least affected genotype by NaCl concentrations was Beyaz. Germination and seedling growth were inhibited at 10 dS/m and above. It was observed that NaCl depressed seedling growth of the genotypes rather than germination because five genotypes germinated but did not have root and shoot to be measured. Moreover, it was concluded that hull ratio of the seed was an effective factor for germination regardless of NaCl levels. It was evaluated that a positive and significant correlation (r=0.692**) between hull ratio and water uptake is an important clue for delaying germination.

/pdf/bazi-cerezlik-aycicegi-helianthus-annuus-l-genotiplerinin-2a7e6c3j8e.pdf

Bazı Çerezlik Ayçiçeği (Helianthus annuus L.) Genotiplerinin Çimlenmesi Üzerine NaCI Konsantrasyonlarının Etkileri

Bu arastirma, farkli humik asit (HA) dozlarinin (kontrol (su), 60, 120 ve 180 g/100 kg tohum) ayciceginde fide gelisimi uzerine etkilerini belirlemek amaciyla 2003 yilinda Ankara Universitesi Ziraat Fakultesi Tarla Bitkileri Bolumunde yurutulmustur. Arastirmada materyal olarak Sanbro, Isera ve P-4223 aycicegi cesitlerine ait tohumlar ile ticari ismi Delta Plus 15 (150 g/l HA + 30 g/l potasyum oksit) olan HA kullanilmistir. Arastirmada, cikis orani, kok ve fide uzunlugu, kok ve fidenin yas ve kuru agirlik degerleri belirlenmistir. Arastirma sonuclarina gore; cikis orani cesitlere ve HA dozlarina gore degismemis ve tum uygulamalarda % 100 cikis elde edilmistir. Kok uzunlugu, HA dozlarina gore 8.43–11.23 cm arasinda degismis ve en yuksek kok uzunlugu 60 g dozdan elde edilmistir. Cesitler arasinda fide boyu bakimindan onemli fakliliklar belirlenmis ve en yuksek deger 8.15 cm ile Sanbro cesidinden elde edilmistir. Uygulanan HA dozlari fide boyunu kontrole gore artirmis ve en yuksek deger 60 g HA dozunda saptanmistir. Kok yas agirligi bakimindan cesitlerin HA dozlarina gosterdigi tepkiler farkli olmustur. Fide yas agirliginda her uc cesitte de 60 g HA dozu daha yuksek sonuclar vermistir. Fide kuru agirligi bakimindan Sanbro cesidi diger cesitlere, HA uygulamalari da kontrole gore ustunluk saglamistir. Arastirma sonucunda, cesitler arasinda fide gelisimi yonunden onemli farkliliklar belirlenirken, ekimden once tohumlarin 60 g HA/100 kg tohum ile muamele edilmesinin ayciceginde fide gelisimini olumlu yonde etkiledigi sonucuna varilabilir

/pdf/f-arkli-humik-asit-dozlarinin-ayciceginin-helianthus-annuus-22w8nim26s.pdf

Özer Kolsarici

Papers

Seed treatments to overcome salt and drought stress during germination in sunflower (Helianthus annuus L.)

Seed yield and oil content of some sunflower (Helianthus annuus L.) hybrids irrigated at different growth stages

Effects of different row distances and various nitrogen doses on the yield components of a safflower variety.

Bazı Çerezlik Ayçiçeği (Helianthus annuus L.) Genotiplerinin Çimlenmesi Üzerine NaCI Konsantrasyonlarının Etkileri

F arklı Humik Asit Dozlarının Ayçiçeğinin (Helianthus annuus L.) Çıkış ve Fide Gelişimi Üzerine Etkileri