Drought stress responses in tolerant and sensitive varieties of black pepper (Piper nigrum Linn.)

Stress responses towards drought was studied in drought tolerant (Panniyur 5) and sensitive (Panniyur 1) varieties of black pepper. On exposure to 15 days (incipient wilting) of drought, Panniyur 1 (P1) showed low RWC of leaves, highly reduced ψs and decrease in the capacity to synthesize sugars and proline as compared to Panniyur 5 (P5). These features indicate the reduced potential of P1 to tolerate long periods of drought as compared to P5. The malondialdehyde content was found to be significantly higher in P1 when compared to P5 during drought. The activity of antioxidant enzymes (guaiacol peroxidase and superoxide dismutase) were found to be low in P1 as compared to P5 at different stages of drought stress, indicating that P1 is comparatively less shielded than P5 from the deleterious effects of reactive oxygen species generated as a result of drought exposure. The photosystems and mitochondria of P1 were more sensitive to drought as compared to that of P5. The effective control of lipid peroxidation and better osmotic adjustments in cells of tolerant variety (P5) may be the prime factors for the increased tolerance of photosystem and mitochondrial systems towards drought stress

Distribution of Bio-accumulated Cd and Cr in two Vigna species and the Associated Histological Variations

In nutrient culture experiments, bioaccumulation and anatomical effects of cadmium (CdCl2 - 20μM) and chromium (K2Cr2O7 - 600 μM) on the structure of root and stem was studied by histochemical and analytical methods in Vigna radiata and Vigna unguiculata. Each metal exerted specific influences on the anatomy of various tissues in root and stem. Histochemical localisation of cadmium and chromium was observed in the stained sections of root and stem. Atomic Absorption Spectrophotometric study revealed maximum accumulation of cadmium and chromium in the root tissue as compared to shoot with significant variation among the species. Abundant occurrences of densely stained deposits of chromium were seen in the root stelar region of V. unguiculata and to a lesser extend in V. radiata. Cadmium accumulation in V. radiata was comparatively more than that of V. unguiculata. The findings also revealed that the accumulation pattern of cadmium and chromium varies between species and hence is species specific

Accumulation Pattern of Heavy Metals in Chromolaena odorata (L.) King & Robins. Grown in Nutrient Solution and Soil

Accumulation pattern of Al, Cd, Fe, Hg, Cr, Cu, Pb, Ni and Zn in Chromolaena odorata plants grown in Hoagland nutrient solution and soil contaminated with known quantities of the above said metals was investigated. Significant variations in the quantity of accumulation as well as distribution among plant parts like root, stem and leaf were shown between the metals. Accumulation of Pb was maximum in the root followed by Fe and Al. Maximum quantity of each metal was accumulated in the root as compared to stem and leaf. Drastic differences in the accumulation pattern of metals between the nutrient solution and soil culture was observed. Comparatively small quantity of metal was accumulated in the plants of soil despite several fold quantity of each metal was given. The results are discussed in terms of BCF, TF, metal specificity as well as detoxification mechanisms

6-Benzylaminopurine Alleviates the Impact of Cu2+ Toxicity on Photosynthetic Performance of Ricinus communis L. Seedlings

Copper (Cu) is an essential element involved in various metabolic processes in plants, but at concentrations above the threshold level, it becomes a potential stress factor. The effects of two different cytokinins, kinetin (KIN) and 6-benzylaminopurine (BAP), on chlorophyll a fluorescence parameters, stomatal responses and antioxidation mechanisms in castor (Ricinus communis L.) under Cu2+ toxicity was investigated. Ricinus communis plants were exposed to 80 and 160 MCuSO4 added to the growth medium. Foliar spraying of 15 M KIN and BAP was carried out on these seedlings. The application of these cytokinins enhanced the tissue water status, chlorophyll contents, stomatal opening and photosynthetic efficiency in the castor plants subjected to Cu2+ stress. The fluorescence parameters, such as Fm, Fv/Fo, Sm, photochemical and non-photochemical quantum yields, energy absorbed, energy trapped and electron transport per cross-sections, were more efficiently modulated by BAP application than KIN under Cu2+ toxicity. There was also effective alleviation of reactive oxygen species by enzymatic and non-enzymatic antioxidation systems, reducing the membrane lipid peroxidation, which brought about a relative enhancement in the membrane stability index. Of the various treatments, 80 M CuSO4 + BAP recorded the highest increase in photosynthetic efficiency compared to other cytokinin treatments. Therefore, it can be concluded that BAP could effectively alleviate the detrimental effects of Cu2+toxicity in cotyledonary leaves of R. communis by effectively modulating stomatal responses and antioxidation mechanisms, thereby enhancing the photosynthetic apparatus’ functioning

Biostimulant priming in Oryza sativa: a novel approach to reprogram the functional biology under nutrient-deficient soil

Biostimulants can be used as an alternative to fertilizers to overcome the effect of nutrient deficiency in plants. Yeast is a biostimulant, having the capacity to modify physiological processes in plants by improving germination and seedling growth under environmental stress. The effects of yeast extract, a sustainable biostimulant derived from yeast (Saccharomyces cerevisiae) containing all the nutritive values, amino acids, vitamins, and growth factors, were investigated in rice (Oryza sativa). Various growth parameters, Chlorophyll a fluorescence, PS II, metabolites accumulation, and antioxidative function of enzymatic (SOD, CAT, APX, GPOX) as well as non-enzymatic (phenol, AsA, and GSH) antioxidant were analyzed in two rice varieties (Hraswa-tolerant and Manu ratna-sensitive) in both yeast extract primed and non-primed seeds subjected to nutrient-deficient soil conditions. The application of the biostimulant (yeast extract) as a priming agent increased the biomass, photosynthetic pigment, modified chlorophyll a fluorescence-related parameters, and also enhanced the photosystem activities of seedlings, supported by decreased content of ROS and MDA in primed seeds when compared to non-primed ones. These changes were accompanied by a significant enhancement in osmolytes and non-enzymatic antioxidants (AsA, GSH, and total phenolics). In general, yeast priming under nutrient-deficient conditions appeared to stimulate the activities of SOD, CAT, and APX in var. Hraswa while GPOX was dramatically upregulated in var. Manu ratna. Thus, these results speculate that yeast priming under nutrient-deficient conditions maintained cell homeostasis and provided better adaptation to the stress conditions in both tolerant as well as sensitive varieties of rice seedlings

Enhanced phytostabilization of cadmium by a halophyte—<i>Acanthus ilicifolius</i> L.

<p>Heavy metal pollution in mangrove wetlands has become a growing matter of concern as it serves as sink and source for toxic heavy metals including cadmium (Cd). The present study evaluates the phytostabilization potential of a halophyte, <i>Acanthus ilicifolius</i> L., toward Cd under hydroponic culture conditions. Accumulation, translocation, and effects of Cd on the antioxidant system of <i>A. ilicifolius</i> were studied. Results indicated that A. ilicifolius accumulated Cd mainly in roots (96.4%) as compared to stem (1.4%) and leaves (0.6%) and the accumulated Cd is retained in root rather than being translocated to shoots as indicated by TF < 0.26. Moreover, malondialdehyde (MDA) content increased upon Cd treatment, which is further detoxified by the enzymatic and nonenzymatic antioxidant mechanism. Antioxidants like proline, ascorbate, and amino acid recorded an increased accumulation in the Cd-treated plants followed by the upregulation of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX). Therefore, the rate of sugar accumulation was found to be decreased in plants treated with Cd as compared to the control plants. Thus, having relatively high BCF_root (69.3) and low TF_shoot (0.26) values, <i>A. ilicifolius</i> can be suggested as a potential candidate for phytostabilization of Cd in mangrove wetlands.</p

Influence of Desiccation and Associated Metabolic Changes During Seed Germination in Corypha umbraculifera Linn.

Corypha umbraculifera L. is a monocarpic palm, which usually flowers after 30-60 years of growth. In C. umbraculifera seeds are the only propagating unit, but the germination rate is very low and seeds are highly recalcitrant. In this context, it was imperative to investigate the desiccation sensitivity, physiological and biochemical changes accompanying the desiccation and germination in C. umbraculifera seeds. Therefore, to make a detailed study, freshly collected C. umbraculifera seeds were desiccated at room temperature for a period of 35 d and physiological and biochemical changes during desiccation and germination were monitored at an interval of 7 d. It was observed that there was a sharp decline in the moisture content of the seed as desiccation proceeded. As the desiccation period progressed, the germination percentage decreased which was below 50% after 35 d. The dry weight percentage of the embryo and endosperm increased with the desiccation period and the increase in dry weight of embryo was significant in comparison with the endosperm. Total protein content of embryo was more compared to that of the endosperm. Peroxidase activity in the embryo was increased up to 28 d of desiccation and decreased further. The endosperm registered a gradual reduction of peroxidase activity during desiccation. In contrast, SOD activity in the embryo was comparatively higher in the fresh seeds and further declined during desiccation, while that of the endosperm remained almost unaltered. The results give a strong indication that desiccation in C. umbraculifera is accompanied by abundant activity of peroxidase in embryo, thereby viability is retained up to 35 days. Whereas, feeble activity of SOD is not seen to be linked with seed viability of C. umbraculifera

Experimental Evidence for Ascorbate-Dependent Electron Transport in Leaves with Inactive Oxygen-Evolving Complexes1[OA]

Previously, we showed that in barley (Hordeum vulgare) leaves with heat-inactivated oxygen-evolving complexes, photosystem II (PSII) has access to a large pool of alternative electron donors. Based on in vitro data, we proposed that this donor was ascorbate, yet this hypothesis has not been substantiated in vivo. In this paper, with the aid of chlorophyll a fluorescence induced by short (5-ms) light pulses and 820-nm absorbance transient measurements on wild-type and ascorbate-deficient (vtc2-1) mutant leaves of Arabidopsis (Arabidopsis thaliana), we show that in heat-treated leaves the rate of electron donation to PSII as well as the 3-(3,4-dichlorophenyl)-1,1-dimethylurea-sensitive electron transport toward photosystem I depend on the ascorbate content of the leaves: upon ascorbate treatment, the donation half-time in the wild type and the mutant decreased from 25 to 22 ms and from 55 to 32 ms, respectively. Thermoluminescence measurements show that TyrZ+ is involved in the electron transfer from ascorbate to PSII. These data and the similar ascorbate dependencies of the heat-treated and the tris(hydroxymethyl)aminomethane-treated thylakoid membranes, with maximal donation half-times of about 16 ms, show that ascorbate is capable of supporting a sustained electron transport activity in leaves containing inactivated oxygen-evolving complexes. This alternative electron transport appears to be ubiquitous in the plant kingdom and is present in the green alga Chlamydomonas reinhardtii, and its rate depends on the physiological state of the plants and on environmental conditions. Our data suggest that ascorbate, as an alternative PSII electron donor, plays a physiological role in heat-stressed plants

Physio-anatomical modifications and elemental allocation pattern in Acanthus ilicifolius L. subjected to zinc stress.

Physio-anatomical modifications and elemental distribution pattern in Acanthus ilicifolius subjected to Zn stress were analysed in this study. Survival of A. ilicifolius plants under a high concentration of ZnSO4 was compensated by the reduction in the photosynthetic efficacy. Micro and macro-elemental distribution pattern in the root tissues was significantly influenced by heavy metal exposure. Tolerance towards the excess toxic metal ions in the tissue of A. ilicifolius was aided by the modified anatomical features. Moreover, the increased deposition of Zn around the central vasculature of the root confirms the complexation of Zn2+ in the xylem vessels. Metal induced molecular level changes of root and leaf samples indicate the presence of OH, NH2, and CH3 deformation as well as C-O-H and C-O-C stretch. A prominent band corresponding to CH3 deformation, pointing hemicellulose fortification, occurs in the cell walls of the xylem, aiding in Zn localization. The phytostabilisation potential of A. ilicifolius is dependent on the coordinated responses which endow with phenotypic plasticity necessary to cope with Zn toxicity

Modulations in Chlorophyll a Fluorescence Based on Intensity and Spectral Variations of Light

Photosynthetic efficiency is significantly affected by both qualitative and quantitative changes during light exposure. The properties of light have a profound effect on electron transport and energy absorption in photochemical reactions. In addition, fluctuations in light intensity and variations in the spectrum can lead to a decrease in photosystem II efficiency. These features necessitate the use of a simple and suitable tool called chlorophyll a fluorescence to study photosynthetic reactions as a function of the aforementioned variables. This research implies that chlorophyll a fluorescence data can be used to determine precise light conditions that help photoautotrophic organisms optimally function