RESUMO
Introduction: The level of fatty acid unsaturation in seeds is one of the major determinants of cold germination ability, particularly in oilseeds. The presence of cis double bonds in unsaturated fatty acids creates bends that lowers their melting temperatures compared to saturated fatty acids. Unsaturated fatty acids with low melting points mobilize faster at low temperatures providing seeds with sufficient energy for germination. Methodology: To investigate the effects of fatty acid unsaturation on the ability of cotton seeds to germinate under cold conditions, four recombinant inbred lines (RILs) of cotton with unique fatty acid profiles were evaluated using a set of developmental and biochemical assays at 12°C (critically low temperature), 15°C (cardinal minimum temperature) and 30°C (optimum temperature). Furthermore, whole seed lipidome profiling using liquid chromatography with mass spectrometry was done to compare the lipid compositional changes at 12°C and 30°C after imbibing cotton seeds of all the six genotypes for 0 hours, 3 hours and 6 hours. Results and discussion: The RILs with higher unsaturation/saturation ratios registered robust germination performance, lower solute leakage, and optimum water uptake rates under cold stress. Imbibition at 30°C for 8 hours before cold exposure significantly improved the germination of cold sensitive genotypes, indicating that the first few hours of water uptake are critical for cold stress. Whole seed lipidome profiling of all the genotypes specifically associated cold germination ability with higher unsaturation levels of phospholipids during early imbibition. The presence of cis double bonds in phospholipids creates kinks that maintain the fluidity of cell membranes under low temperature. Membrane flexibility under cold conditions is essential for facilitating key germination events including membrane organization and respiration. The current results highlight the importance of fatty acid composition in cold germination ability of upland cotton.
RESUMO
Cold stress breeding that focuses on the improvement of chilling tolerance at the germination stage is constrained by the complexities of the trait which involves integrated cellular, biochemical, hormonal and molecular responses. Biological membrane serves as the first line of plant defense under stress. Membranes receive cold stress signals and transduce them into intracellular responses. Low temperature stress, in particular, primarily and effectively affects the structure, composition and properties of cell membranes, which ultimately disturbs cellular homeostasis. Under cold stress, maintenance of membrane integrity through the alteration of membrane lipid composition is of prime importance to cope with the stress. This review describes the critical role of cell membranes in cold stress responses as well as the physiological and biochemical manifestations of cold stress in plants. The potential of cell membrane properties as breeding targets in developing strategies to improve cold germination ability is discussed using cotton (Gossypium hirsutum L.) as a model.
RESUMO
The objective of the present study was to determine heat stress zones (HSZ) in a year for daily milk yield (DMY) of Murrah buffaloes. Data for the study included 2,67,599 daily milk yield records of 445 Murrah buffaloes sired by 171 bulls as well as climatic parameters, viz. dry bulb temperature (Tdb) and wet bulb (Twb) temperatures spanning over 16 years (2001-2016). The regression analysis of DMY on carryover heat effect indicated that the decline in DMY was significant above the carryover heat effect (CHE) 70. April-November were critical for daily milk yield, and maximum decline in daily milk yield was observed during the month of August in Murrah buffaloes. Therefore, two zones in a year were classified as non-heat stress zone (NHSZ) with CHE < 70 for months December-March and heat stress zone (HSZ) with CHE > 70 during April-November.
