Jagmeet Kaur

Heat Stress at Reproductive Stage Disrupts Leaf Carbohydrate Metabolism, Impairs Reproductive Function, and Severely Reduces Seed Yield in Lentil

ABSTRACT Rising temperatures or global warming will be detrimental for various crops. Moreover, because of increasing demand for lentil (Lens culinaris L.) grains, there is a need to broaden the adaptation of this crop into warmer climes. Hence, a study was conducted to evaluate the effects of high temperatures (>32/20oC) during reproductive growth on performance of lentil and to probe the mechanisms associated with reproductive failures. Three lentil genotypes, viz., LL699, LL931, and LL1122, were grown in pots at two sowing dates: (1) the normal sowing time (NS) in November so that day/night temperatures during the reproductive stage were below 32/20°C; and (2) late-sown (LS) in February so that temperatures during the reproductive stage were above 32/20°C. The plants were fully irrigated during both the sowing situations. In LS plants, the phenology was accelerated, leading to substantial reduction in biomass, flowers, and pods, accompanied by marked shortening of flowering period and podding duration, causing decreased seed yield. At the peak flowering stage (average temp. >32/23oC), the leaves of the LS plants had significantly lower relative leaf water content and lower stomatal conductance than NS plants at the same stage, indicating that the late sowing induced both water stress and heat stress. In LS plants, reproductive function was markedly reduced in all genotypes, causing increased pod abortion. The leaves of LS plants showed increased damage to membranes, chlorosis, decreased photochemical efficiency, with an associated reduction in sucrose synthesis and increase in its hydrolysis, compared with the NS plants. Heat stress, in combination with intermittent water stress during the reproductive phase in the LS plants, was extremely detrimental for all three lentil genotypes, with only minor differences among them. Controlled-environment studies, where the plants were subjected to high temperatures (33/15°C, 35/20°C) during reproductive growth, also validated the detrimental effects of heat stress on studied traits, similar to outdoor conditions.

Phylogenetic diversity of Mesorhizobium in chickpea

Crop domestication, in general, has reduced genetic diversity in cultivated gene pool of chickpea (Cicer arietinum) as compared with wild species (C. reticulatum, C. bijugum). To explore impact of domestication on symbiosis, 10 accessions of chickpeas, including 4 accessions of C. arietinum, and 3 accessions of each of C. reticulatum and C. bijugum species, were selected and DNAs were extracted from their nodules. To distinguish chickpea symbiont, preliminary sequences analysis was attempted with 9 genes (16S rRNA, atpD, dnaJ, glnA, gyrB, nifH, nifK, nodD and recA) of which 3 genes (gyrB, nifK and nodD) were selected based on sufficient sequence diversity for further phylogenetic analysis. Phylogenetic analysis and sequence diversity for 3 genes demonstrated that sequences from C. reticulatum were more diverse. Nodule occupancy by dominant symbiont also indicated that C. reticulatum (60%) could have more various symbionts than cultivated chickpea (80%). The study demonstrated that wild chickpeas (C. reticulatum) could be used for selecting more diverse symbionts in the field conditions and it implies that chickpea domestication affected symbiosis negatively in addition to reducing genetic diversity.

Differential proline metabolism in vegetative and reproductive tissues determine drought tolerance in chickpea

Proline is emerging as a critical component of drought tolerance and fine tuning of its metabolism under stress affects the plants sensitivity and response to stress. Thus the study was carried out to analyse the effect of water deficit on the proline content and principal enzymes involved in its synthesis (Δ1-pyrolline-carboxylate synthetase) and catabolism (proline dehydrogenase) at different developmental stages and in different organs (roots, nodules, leaves, pod wall, and seeds) of two chickpea (Cicer arietinum L.) cultivars differing in drought tolerance (drought tolerant ICC4958 and drought sensitive ILC3279). It was observed that increased Δ1-pyrolline-carboxylate synthetase activity under moderate stress in roots and nodules of ICC4958 caused an increase in proline content during initiation of reproductive development whereas increased proline dehydrogenase activity in nodules and leaves at this period helped to maintain reducing power and energy supply in tissues and proper seed development as seed biomass increased consistently up to maturity. On the other hand, roots and nodules of ILC3279 responded to stress by increasing proline content after the developmental phase of reproductive organs was over (near maturity) which negatively affected the response of pod wall to stress. Concurrent increase in activities of Δ1-pyrolline-carboxylate synthetase and proline dehydrogenase in pod wall of ILC3279 aggravated the oxidative stress and affected seed development as seed biomass initially increased rapidly under stress but was unaffected near maturity.

Nodule metabolism in cold stress tolerant and susceptible chickpea cultivars

Early maturing short duration cold-tolerant chickpea cultivars are being introduced to avoid yield loss from spell faced by crops. However, the biochemical basis of the low temperature stress tolerance is not known. In the present study carbon and nitrogen metabolizing enzymes in nodules along with physiological indices were measured in early maturing short duration cold- tolerant chickpea cultivars (ICCV 93929 and ICCV 88503) and in normal cold - susceptible (PBG1 and GPF2) cultivars. The higher biomass in nodules of cold-tolerant cultivars might act as a greater sink for attracting photoassimilates to fuel N2-fixation. The simultaneous increase of sucrose synthase and alkaline invertase in nodules of ICCV 93929 and ICCV 88503 at the stage corresponding to lower temperature, ensures hexose supply for meeting the energy and reducing power demands for active nitrogen fixation. The greater activity of glutamine synthetase observed in nodules of cold tolerant cultivars at stages exposed to lower temperature indicates an efficient assimilation of the symbiotically fixed nitrogen into amino acids. The total protein and amino acid contents were also higher in cold tolerant cultivars. There was a greater and more rapid dry matter accumulation in ICCV 88503 and ICCV 93929 as compared to PBG1 and GPF2 in which biomass accumulation extended up to 70 DAS. Sustainable photosynthetic efficiency and activities of carbon and nitrogen metabolizing enzymes for a longer period in ICCV 93929 and ICCV 88503 even after flowering and during the onset of pod setting indicates that period of active nitrogen fixation is extended in cold tolerant chickpea cultivars due to allocation of photosynthates for longer period. This will lead to more transfer of reduced N as amino compounds towards the shoots which will lead to more nitrogen availability to seeds and ultimately better seed filling. The molecular diversity characterized by using RAPD primers and clustering method revealed a greater similarity between cold tolerant cultivars than between the cold susceptible cultivars.

Growth and yield in chickpea (Cicer arietinum L.) genotypes in response to water stress

-1 , leaf area, leaf area index were recorded at 120 days after sowing (DAS) which showed significant variation with water stress at varied growth stages. The maximum reduction in height and branches was observed when irrigation was restricted at T2 stage. Restricted irrigation decreased the biomass of stem, leaves and roots leading to reduced leaf area and leaf area index as well. The yield traits viz. 100 seed weight, total number of pods, percentage filled pods were reduced significantly under stress. The grain yield under restricted conditions was reduced by 40.50 to 55.91% over irrigated control in T4 to T2, respectively. Among the tested genotypes, GL28151, RSG963, PDG3 maintained higher growth, yield and yield traits showing their tolerance to water stress, while GL22044, RSG1861 and RVSSG4 were adversely affected most in growth traits and yield as well.

Free radical scavenging activities can mitigate the effect of water stress in chickpea

Abstract. To get a comprehensive view of drought tolerance mechanisms, the influence of water deficit stress on antioxidative capacity due to scavenging of free radicals and ability to maintain reduced cell state was investigated in roots, nodules, leaves, pod wall and seeds of two chickpea cultivars differing in rooting behaviour. ICC4958 (deep rooted) possessed better ability to combat water deficit-induced oxidative stress relative to ILC3279 (shallow rooted) as revealed by increase in total phenol, reducing power, ferric reducing ability and capacity to scavenge 2,2-Diphenyl-1-picryl hydrazyl (DPPH) and OH free radicals. Effect of water deficit stress on photosynthetic pigments of these cultivars was also studied. The investigation revealed that the influence of water stress in enhancing antioxidative capacity was most prominent in roots of ICC4958 among all other tissues as revealed by increased total phenols, DPPH and OH free radical scavenging activity and total reducing power under stress. However, roots of ILC3279 suffered a decrease in total phenolic content, total reducing power and DPPH free radical scavenging activity under prolonged stress, which was reflected in reduced antioxidative defence in reproductive tissues like decreased reducing power in pod wall and ferric-reducing antioxidant power ability in seeds.

Water deficit stress tolerance in chickpea is mediated by the contribution of integrative defence systems in different tissues of the plant

Drought induces heavy yield losses in chickpea (Cicer arietinum L.). Besides understanding the physiological and biochemical parameters contributing to drought tolerance, we need to understand the importance of one tissue in combatting drought stress-induced oxidative stress and influencing the antioxidative defence system in other tissues. The study was conducted to examine the influence of drought stress conditions on the antioxidative defence system and physiology in different tissues such as roots, leaves, nodules, pod walls and seeds at various vegetative and reproductive growth stages in two chickpea cultivars differing in rooting behaviour: ICC4958 (deep rooted) and ILC3279 (shallow rooted). The traits contributing to drought tolerance in ICC4958 were increased root area, decreased leaf area index or increase in root area, decreased leaf area; ILC3279 displayed a decrease in root area and an increase in LAI. The adaptation of ICC4958 was also accompanied by biochemical adjustments, like increases in antioxidative enzymes (superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase and catalase) and nonenzymatic antioxidants (ascorbic acid, proline and stress-induced proteins). However, increases in antioxidant enzymes, nonenzymatic antioxidants and proteins in ILC3279 were lower than in ICC4958. The lower malondialdehyde content and membrane permeability index in ICC4958 might be responsible for reduced damage under drought stress. Increased H2O2 content in ICC4958 was related to enhanced antioxidative defence, emphasising its role as a signalling molecule under stress. This is the first study conducted on drought stress-induced enzymatic and nonenzymatic antioxidative defence systems in underground, aboveground vegetative and reproductive tissues in chickpea cultivars differing in rooting behaviour.

Variation of morpho-physiological traits in geographically diverse pigeonpea [Cajanus cajan (L.) Millsp] germplasm under different phosphorus conditions

ABSTRACT Genotypic variation for morpho-physiological parameters, phosphorus (P) content and root acid phosphatase activity was studied in 52 pigeonpea genotypes. Data related to shoot (length, dry weight, number of leaves, and leaf area), root (volume, length, dry weight, area, perimeter, and number of root tips), acid phosphatase activity, and P content (root, stem, and leaf) were recorded at 60 days after sowing (DAS). The P use efficient genotypes showed high root length, root area, root perimeter, root dry weight, P content in leaves, and root to shoot dry weight ratio under the P not added condition. Significant variation was found among genotypes for root- and shoot-associated characteristics under both P treatments. The P use efficient genotypes with improved root morphological phenes have potential to acquire and utilize more P from immobile soil bound P sources may be of additional factor for increasing efficiency of acquisition and utilization of supplied P fertilizer.

Genetic variation for tolerance to post-emergence herbicide, imazethapyr in lentil (Lens culinaris Medik.)

ABSTRACT Weeds pose a serious constraint to lentil production. Identification and deployment of post-emergence herbicide tolerance in improved varieties can help reduce the production cost and increase the productivity and area under lentil cultivation. Imazethapyr, a post-emergence herbicide was tested on 180 lentil genotypes for two consecutive years. Significant variation among the genotypes was observed for tolerance to imazethapyr. On a 1–5 scale, 12 genotypes were found tolerant, 46 moderately tolerant, 112 sensitive and 10 highly sensitive during the first season, and 11 genotypes were found tolerant, 51 moderately tolerant, 110 sensitive and 8 highly sensitive during the second season. Based on the first year’s result, 30 genotypes, representing tolerant, moderately tolerant, sensitive and highly sensitive reactions, were evaluated to determine the effect of herbicide on morpho-physiological and yield traits. The adverse effect of imazethapyr was significant on growth and yield attributes of lentils. Five genotypes namely LL699, LL1397, IPL406, EC78452 and LL1203 demonstrated tolerance to imazethapyr with limited phytotoxic effect on various morpho-physiological traits. These genotypes showed less reduction (<19%) for seed yield in imazethapyr treated plots as compared to control. These genotypes offer scope for developing post-emergence herbicide tolerant cultivars in lentil.

Translocation of metabolites in pigeonpea (Cajanus cajan L.) under the influence of mineral nutrients

Mineral nutrient sources viz., CaCl2 (0.01% and 0.02%), KNO3 (0.5% and 1%), MgCl2 (0.1% and 0.2%) and urea (1% and 2%) were applied as foliar application to pigeonpea varieties (PAU 881 and AL 201) at green floral bud stage of inflorescence to study their effect on the level of various metabolites viz., total soluble sugars, total starch, total free amino acids and total soluble proteins in leaves and their subsequent accumulation in developing seeds. It was observed that mineral nutrients caused greater accumulation of different metabolites in developing seeds (sink) which may be attributed to enhanced translocation of these metabolites from source to sink tissues as evident from their decline in leaf tissues (source) thereby strengthening the source-sink relationship in pigeonpea. Urea application @ 2% increased accumulation of metabolites in mature seeds by 27.71 (PAU 881) and 25.25% (AL 201) in case of total soluble sugars, 11.19 (PAU 881) and 11.33%(AL 201) in case of total starch, 38.23 (PAU 881) and 39.41% (AL 201) total free amino acids and 10.72 (PAU 881) and 8.66% (AL 201) of total soluble proteins as compared to their respective controls.