Role of Abscisic Acid, Leaf Hydraulic Conductance and Associated Genes in Conferring Drought Tolerance to Naked Oat (Avena nuda L.)

Abstract

Role of Abscisic Acid, Leaf Hydraulic Conductance and Associated Genes in Conferring Drought Tolerance to Naked Oat (Avena nuda L.) The prevalent drought has caused a decline in the production of major cereal grains. Naked oats are fetching more attention of the farmers and consumers as they require less soil nutrients and water than major cereal crops whereas, possess greater nutrition. There is limited knowledge about the effects of leaf hydraulic conductance (Kleaf), abscisic acid (ABA) accumulation, and synthesis by the leaves during drought on the yield and the post drought recovery of Kleaf and leaf physiology. The present study compared the naked oat cultivars Dy7 and Ym for their drought tolerance by comparing the growth, physiology, and yield responses under different water treatments. The water treatments included (a) terminal drought (b) early ephemeral drought (c) different field water capacities of 90 %, 60 %, 40 % and 20 %, (d) normal irrigation in control (C) plants and (e) their post drought recovery by rewatering. The plants were grown in completely randomized design (CRD). The cultivars were tested for their physiological responses including the leaf water potential (Ѱleaf), (Kleaf), gaseous exchange through stomata (Gs), photosynthesis (Pn), evapotranspiration (E), pollen viability and germination, leaf ABA concentration, NCED2 and ABA 8’ OH2 expression during dehydration. The growth responses included the leaf area (LA), leaf number (LN), plant height (PH), root length (RL) and flower number (FN). The results revealed that the Ѱleaf declined gradually for both cultivars during drought, nonetheless Dy7 leaves could tolerate more negative Ѱleaf. Under 40 % FC the midday Ѱleaf decreased significantly for Ym plants. The midday Ѱleaf and Kleaf also declined under the effect of age in the normal irrigated plants but Dy7 sustained these activities as compared with Ym. The kmax values were 6.6577 mmolm-2 s -2MPa-1 and 7.167863 mmolm-2 s -2MPa-1 for Ym and Dy7 respectively. The p50 differed significantly for the two cultivars under the effect of drought. Physiological activities declined with reduction in soil moisture content, Pn, E and Gs declined as Ѱleaf declined to -1 MPa and so on. The expression of NCED2 increased immediately in both the cultivars xii under water stress, the highest fold change at - 3.5 MPa was 8.5 ± 0.15 and 4.2 ± 0.13 in Dy7 and Ym leaf samples respectively. However, ABA8′OH2 expression decreased by 1 fold due to drought showing significant decline at p < 0.05. The highest % germinated pollens recorded for well-watered (WW) Dy7 was 86 ± 2.65, while for WW plants of Ym it was 81 ± 2.65 %, the mean viable pollens % was 85 ± 2.65 % while 83 ± 2.65 % respectively. The cultivar Dy7 maintained higher pollen germination and pollen viability under drought stress in comparison with Ym. The greatest mean TKW was recorded as 6 ± 1.7 g/plant in WW Dy7 while 3 ± 1.5 g/plant for water stressed (WS) plants, on the other hand 4 ± 2.5 g/plant for Ym WW plants and 2 ± 1.5 g/plant for WS Ym plants that was significantly lower than WW Ym plants. The mean number of grains produced by the C plants was 323.6 ± 10.5 and 279.4 ± 10.3 for Dy7 and Ym respectively, whereas the WS plants at FC 20 % produced significantly (p < 0.05) lower number of grains of 152.4 ± 7 and 100.8 ± 2.6 grains by Dy7 and Ym plants respectively. In current study, leaf hydraulic conductance and NCED2 gene appeared as important determinants for better drought tolerance of Dy7 plants in comparison with Ym. Keywords: Hydraulic conductance, Avena nuda, Stomatal conductance, Drought, Recovery, Gene, Leaf water potential