Plant physiology

About: Plant physiology is a research topic. Over the lifetime, 1537 publications have been published within this topic receiving 72038 citations.

Impact of excess zinc on growth parameters, cell division, nutrient accumulation, photosynthetic pigments and oxidative stress of sugarcane (Saccharum spp.)

Abstract: The present study employed a sand culture experiment with three levels of zinc viz., 0.065 (control), 65.0 and 130 mg l−1 Zn (excess) as zinc sulfate, respectively, in sugarcane (Saccharum spp.), cultivar CoLk 8102. The results indicated growth depression, dark green leaves, decreased root number and length and sharp depression in mitotic activity of roots due to high doses of Zn (65 and 130 mg l−1); effects were significant at 130 mg l−1 Zn supply. The endogenous ion contents measurements revealed roots to be the major sink for excess Zn with lower amounts in leaves of sugarcane plants. High level of Zn decreased total phosphorus in leaves and increased it in roots. Fe and Cu content decreased, while, Mn increased in sugarcane plants due to high Zn in the growing medium. Plants experienced oxidative stress when exposed to higher levels of zinc. Biochemical investigations indicated high level of hydrogen peroxide, malondialdehyde contents with high chlorophyll a, b and carotenoids contents and activity of superoxide dismutase, catalase and peroxidase enzymes under high Zn conditions. These findings confirm suggest that excess Zn adversely affects root growth and mitotic efficiency, enhances chromosomal aberrations and increases growth and nutrient accumulation abnormalities, as well as oxidative stress.

Screening of visible and UV radiation as a photoprotective mechanism in plants

Abstract: Prolonged exposure of plants to high fluxes of solar radiation as well as to other environmental stressors disturbs the balance between absorbed light energy and capacity of its photochemical utilization resulting in photoinhibition of and eventually in damage to plants. Under such circumstances, the limiting of the light absorption by the photosynthetic apparatus efficiently augments the general photoprotective mechanisms of the plant cell, such as reparation of macromolecules, elimination of reactive oxygen species, and thermal dissipation of the excessive light energy absorbed. Under stressful conditions, plants accumulate, in different cell compartments and tissue structures, pigments capable of attenuation of the radiation in the UV and visible parts of the spectrum. To the date, four principle key groups of photoprotective pigments are known: mycosporine-like amino acids, phenolic compounds (including phenolic acids, flavonols, and anthocyanins), alkaloids (betalains), and carotenoids. The accumulation of UV-absorbing compounds (mycosporine-like amino acids and phenolics in lower and higher plants, respectively) is a ubiquitous mechanism of adaptation to and protection from the damage by high fluxes of solar radiation developed by photoautotrophic organisms at the early stages of their evolution. Extrathylakoid carotenoids, betalains, and anthocyanins play an important role in long-term adaptation to the illumination conditions and in protection of plants against photodamage. A prominent feature of certain plant taxa lacking some classes of photoprotective pigments (such as anthocyanins) is their substitution by other compounds (e.g. keto-carotenoids or betalains) disparate in terms of chemical structure and subcellular localization but possessing close spectral properties.

Enhancement of Carotenoid Biosynthesis in Transplastomic Tomatoes by Induced Lycopene-to-Provitamin A Conversion

Abstract: Carotenoids are essential pigments of the photosynthetic apparatus and an indispensable component of the human diet. In addition to being potent antioxidants, they also provide the vitamin A precursor β-carotene. In tomato (Solanum lycopersicum) fruits, carotenoids accumulate in specialized plastids, the chromoplasts. How the carotenoid biosynthetic pathway is regulated and what limits total carotenoid accumulation in fruit chromoplasts is not well understood. Here, we have introduced the lycopene β-cyclase genes from the eubacterium Erwinia herbicola and the higher plant daffodil (Narcissus pseudonarcissus) into the tomato plastid genome. While expression of the bacterial enzyme did not strongly alter carotenoid composition, expression of the plant enzyme efficiently converted lycopene, the major storage carotenoid of the tomato fruit, into provitamin A (β-carotene). In green leaves of the transplastomic tomato plants, more lycopene was channeled into the β-branch of carotenoid biosynthesis, resulting in increased accumulation of xanthophyll cycle pigments and correspondingly reduced accumulation of the α-branch xanthophyll lutein. In fruits, most of the lycopene was converted into β-carotene with provitamin A levels reaching 1 mg per g dry weight. Unexpectedly, transplastomic tomatoes also showed a >50% increase in total carotenoid accumulation, indicating that lycopene β-cyclase expression enhanced the flux through the pathway in chromoplasts. Our results provide new insights into the regulation of carotenoid biosynthesis and demonstrate the potential of plastids genome engineering for the nutritional enhancement of food crops.

Dynamic acclimation of photosynthesis increases plant fitness in changing environments.

Abstract: Plants growing in different environments develop with different photosynthetic capacities—developmental acclimation of photosynthesis. It is also possible for fully developed leaves to change their photosynthetic capacity—dynamic acclimation. The importance of acclimation has not previously been demonstrated. Here, we show that developmental and dynamic acclimation are distinct processes. Furthermore, we demonstrate that dynamic acclimation plays an important role in increasing the fitness of plants in natural environments. Plants of Arabidopsis (Arabidopsis thaliana) were grown at low light and then transferred to high light for up to 9 d. This resulted in an increase in photosynthetic capacity of approximately 40%. A microarray analysis showed that transfer to high light resulted in a substantial but transient increase in expression of a gene, At1g61800, encoding a glucose-6-phosphate/phosphate translocator GPT2. Plants where this gene was disrupted were unable to undergo dynamic acclimation. They were, however, still able to acclimate developmentally. When grown under controlled conditions, fitness, measured as seed output and germination, was identical, regardless of GPT2 expression. Under naturally variable conditions, however, fitness was substantially reduced in plants lacking the ability to acclimate. Seed production was halved in gpt2− plants, relative to wild type, and germination of the seed produced substantially less. Dynamic acclimation of photosynthesis is thus shown to play a crucial and previously unrecognized role in determining the fitness of plants growing in changing environments.

Contrasting effects of GA3 treatments on tomato plants exposed to increasing salinity.

Abstract: The role of plant hormones under saline stress is critical in modulating physiological responses that will eventually lead to adaptation to an unfavorable environment. Nevertheless, the functional level of plant hormones, and their relative tissue concentration, may have a different impact on plant growth and stress tolerance at increasing salinity of the root environment. Vigorous plant growth may counteract the negative effects of salinization. In contrast, low gibberellin (GA) levels have been associated with reduced growth in response to salinity. Based on these facts and considering that the physiological basis of the cause-effect relationship between functional growth control and stress adaptation/survival is still a matter of debate, we hypothesized that exogenous applications of the plant hormone GA3 may compensate for the salt-induced growth deficiency and consequently facilitate tomato plant adaptation to a saline environment. GA3 application (0 or 100 mg GA3 l−1) was compared under four salinity levels, obtained by adding equal increments of NaCl:CaCl2 (2:1 molar basis) (EC = 2.5, 6.8, 11.7, 16.7 dS m−1) to the nutrient solution. GA3 treatment reduced stomatal resistance and enhanced plant water use at low salinity. These responses were associated with an increased number of fruit per plant at harvest. However, moderate and high salinity nullified these differences. The fruit carotenoid level was generally lower in GA3-treated plants, indicating either an inhibitory effect of GA3 treatment on carotenoid biosynthesis or a reduced perception of the stress environment by GA3-treated tomato plants.