Abstract
Gradually increasing temperatures at global and local scales are causing heat stress for cool and summer-season food legumes, such as lentil (Lens culinaris Medik.), which is highly susceptible to heat stress, especially during its reproductive stages of development. Hence, suitable strategies are needed to develop heat tolerance in this legume. In the present study, we tested the effectiveness of heat priming (HPr; 6 h at 35 °C) the lentil seeds and a foliar treatment of γ-aminobutyric acid (GABA; 1 mM; applied twice at different times), singly or in combination (HPr+GABA), under heat stress (32/20 °C) in two heat-tolerant (HT; IG2507, IG3263) and two heat-sensitive (HS; IG2821, IG2849) genotypes to mitigate heat stress. The three treatments significantly reduced heat injury to leaves and flowers, particularly when applied in combination, including leaf damage assessed as membrane injury, cellular oxidizing ability, leaf water status, and stomatal conductance. The combined HPr+GABA treatment significantly improved the photosynthetic function, measured as photosynthetic efficiency, chlorophyll concentration, and sucrose synthesis; and significantly reduced the oxidative damage, which was associated with a marked up-regulation in the activities of enzymatic antioxidants. The combined treatment also facilitated the synthesis of osmolytes, such as proline and glycine betaine, by upregulating the expression of their biosynthesizing enzymes (pyrroline-5-carboxylate synthase; betaine aldehyde dehydrogenase) under heat stress. The HPr+GABA treatment caused a considerable enhancement in endogenous levels of GABA in leaves, more so in the two heat-sensitive genotypes. The reproductive function, measured as germination and viability of pollen grains, receptivity of stigma, and viability of ovules, was significantly improved with combined treatment, resulting in enhanced pod number (21–23% in HT and 35–38% in HS genotypes, compared to heat stress alone) and seed yield per plant (22–24% in HT and 37–40% in HS genotypes, in comparison to heat stress alone). The combined treatment (HPr+GABA) was more effective and pronounced in heat-sensitive than heat-tolerant genotypes for all the traits tested. This study offers a potential solution for tackling and protecting heat stress injury in lentil plants.
Highlights
Air temperatures are rising at both global and local scale, causing heat stress in many cool and summer season food crops and reducing their production potential [1,2]
Seeds of four lentil genotypes (two heat-tolerant (IG2507, IG3263), two heat-sensitive (IG2821, IG2849)), procured from the Indian Institute of Pulses Research, Kanpur, Uttar Pradesh, India; phenology (Figure 1), were heat primed at 35 ◦C for 6 h in the dark in Petridishes having double-layered filter paper moistened with distilled water in a growth chamber maintained at 35 ◦C and relative humidity of 90% in the dark
The present study revealed that heat priming (HPr) and exogenous application of GABA increased the endogenous GABA concentration, along with several other defense-related mechanisms to reduce the heat stress injury to the leaves and reproductive function resulting in improved yield-related traits
Summary
Air temperatures are rising at both global and local scale, causing heat stress in many cool and summer season food crops and reducing their production potential [1,2]. Heat stress inhibits the growth and development of various food crops by altering several physiological and biochemical processes, which impairs crop performance [2,3]. Heat stress severely impacts the plants by disrupting pollen and stigma function and resulting in the lower seed set percentage [2,4]. The process of fertilization is impacted because of obstruction in pollen development, germination, and tube growth, resulting in pod set failure in different food grain and legumes crops [2,5,6]. Strategies are needed to impart heat tolerance in lentil
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