Water is a major limiting factor in world agriculture and most crop plants are highly sensitive to even a mild water stress.The beneficial effects of diatomite is characterized by helping plants to overcome various biotic and abiotic stresses. Thus , this experiment was performed to study the ameliorative effect of diatomite (10g/kg) on each of growth, productivity, gas exchange , biochemical contents and polymorphic DNA of Lupinus albus L. plants grown in either well watered or two different soil water regimes (1 and 4 days withdrawal). Results showed that diatomite was able to alleviate the deteriorative effect of water stress on almost all measured criteria specially in plants grown under mild water stress (1+D).Soil fertilization by diatomite significantly increased all measured growth parameters expressed as shoot and root length, fresh and dry weight of shoot, root and pods and number of pods/plant above both untreated and water stress -free diatomite treated plants. Diatomite application improved the rate of photosynthesis, stomatal conductance, the contents of each of total soluble sugars (TSS), total soluble protein (TSP) , total phenols, auxins, gibberellins, cytokinins and ABA and the activity of four antioxidant enzymes namely, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and polyphenol oxidase (PPO) as compared to both control and stressed plants maintained at both levels of water regime. On the contrary, diatomite treatment markedly reduced transpiration rate and lipid peroxidation level to a minimum . Moreover, diatomite application either alone or combined with stress induced a distinctive protein electrophoratic band (92KD) which was absent in either the control or stressed plants. Three distinctive protein bands were also induced in stressed white lupin, two (65 and 25 KD) under one day drought and one (143K) under four day drought. Finally, diatomite induced several distinguished polymorphic DNA fragments using PCRRAPD analysis.

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Role of plant growth regulators in agriculture - a physiological approach.

Beneficial effects of diatomite on the growth, the biochemical contents and polymorphic DNA in Lupinus albus plants grown under water stress

Salt toxicity is one of the major problems in modern agriculture. Plants can employ silicon as a protective agent against stresses and the mechanisms of this process remain unknown. Two Egyptian clover (Trifolium alexandrinum) cultivars differing in salinity tolerance were used (Helaly, salt sensitive and Sarw1, salt tolerant). They were grown in pots filled with normal and saline soil (2000 and 3000 ppm) in the absence or presence of diatomites (0, 1.5, 3 and 4.5 g/kg soil). Results indicated that diatomite significantly offset the negative impacts of salinity and increased tolerance of sensitive cultivar of clover (Helaly) to salinity stress. Salinity decreased markedly all measured growth parameters (plant height and fresh and dry weight of fodder/pot), photosynthetic rate , the percentage of relative water content (%RWC), percentage  of membrane stability index (%MSI), total photosynthetic pigment, and the contents of each of magnesium (Mg), potassium (K), phosphorus (P), and calcium (C) while it increased the levels of both amino acids, proline and sodium (Na) in both  T. alexandrinum cultivars, however the effect was more profound on the sensitive line. Addition of diatomite at an upgraded rates solely or combined with both concentrations of NaCl significantly increased the above measured growth parameters, photosynthesis, %RWC, %MSI, total pigment and the accumulation of each of Mg, K, P and Ca. Moreover, it synergistically increased the content of total amino acids while, on the other hand, reduced the contents of proline and Na. Notably, the impact of diatomite in mitigating the deteriorative effect of salinity was clearly manifested more in sensitive lines of clover than in tolerant ones and under the higher dose of salinity (3000 ppm) as compared to the lower dose (2000 ppm). Moreover, diatomite fertilization either alone or interacting with salinity induced two distinctive protein electrophoratic bands (233 and 25 KD) which were absent in either the control or salinity stressed cultivars. In this respect, diatomite was most effective at 3 g/kg on Helaly and 4.5 g/kg on Sarw1 imposed to the higher dose of salinity (3000 ppm). Diatomite application either alone or combined with salinity induced several distinguished amplified DNA fragments in both clover cultivars using PCR- RAPD analysis , although the number of induced polymorphic DNA fragments were more in Helaly than in Sarw1. These results indicate that diatomite recovered and improved the morphologic, metabolic and biochemical status of both cultivars under salinity stress and especially the sensitive line (Helaly).

	 

	Key words: Diatomite, growth, proline, aminoacids, membrane stability index, relative water content, minerals, protein electrophorasis and RAPD-(DNA).

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Impact of diatomite nutrition on two Trifolium alexandrinum cultivars differing in salinity tolerance

2 Abstract: The physiological adaptive features pertaining two different halophytes, Arthrocnemum macrostachyum and Nitraria retusa, inhabiting North and South Sinai Peninsula were investigated during spring and summer. Site1 represents North Sinai (El-Arish region) and site2 representing South Sinai (Ras Sudr region). Site1 was characterized by higher rainfall and lower temperature compared to site2. The soils of both sites are characterized by higher electrical conductivity during summer and their water contents are higher in the lower than the upper horizon. Results showed that A. macrostachyum possessed higher succulence ratio in both seasons compared to N. retusa, while the opposite was true in cell-membrane electrical conductivity. In each species the cell-sap osmotic potential decreased during the summer which was appreciably lower in A. macrostachyum. In summer, A. macrostachyum showed higher levels of photosynthetic pigments (Chl. a, b and carotenoids) compared to those in spring while the opposite was found in case of N. retusa. In each species, the activities of catalase and peroxidase increased during summer, where N. retusa recorded higher activities of catalase than A. macrostachyum in both sites and for peroxidase in site1. Superoxide dismutase activity was higher in spring than summer in N. retusa in both sites but for A. macrostachyum in site1. Ascorbic acid content was significantly higher in both sites during spring in both species, while MDA has accumulated in summer in both sites for N. retusa and in A. macrostachyum in site1. N. retusa has experienced higher proline level in spring at site2. Each species possessed higher nitrogen content during summer in both sites. In each species and in each site, the DNA and RNA contents were significantly higher in spring. A. macrostachyum showed appreciably higher levels of all protein-bound amino acids in spring in site1 and the opposite was true in site2. In N. retusa a similar increase was recorded in the two sites in spring, except for glycine and methionine in site1 and alanine and valine in site2. The SDS-PAGE of the total proteins indicated that during spring and summer seasons A. macrostachyum was characterized by the presence of pe rsistent bands having molecular weights (M W) ~23 and 15.79-16 kDa in site1 and ~15.6 kDa in site2 in both sites, while N. retusa displayed common bands having MW 22.30-22.17and 16.15-16.56 kDa in site1 and ~22 and 16.35 kDa in site2. High molecular weight protein bands appeared in site-2 during spring having MW 96.02 kDa and 103.04 kDa in N. retusa and A. macrostachyum, respectively. In summer, A. macrostachyum showed another bands having M W ranging between 24 and 62 kDa while N. retusa showed five proteins bands having MW ranging between 24 and 70 kDa.

Role of plant growth regulators in agriculture - a physiological approach.

Citations

Beneficial effects of diatomite on the growth, the biochemical contents and polymorphic DNA in Lupinus albus plants grown under water stress

Impact of diatomite nutrition on two Trifolium alexandrinum cultivars differing in salinity tolerance

Physiological Adjustment of Arthrocnemum macrostachyum and Nitraria retusa to Saline Habitats in Sinai, Egypt

Gene expression of heat stress on protein and antioxidant enzyme activities of two Lupinus species.

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