ABSTRACT
This study aimed to investigate the impact of individual drought, heat, and combined drought and heat stress on twelve cotton genotypes, including eight tolerant and four susceptible genotypes. A field experiment was carried out by employing a randomized complete block split-plot design, with treatments (control, drought, heat, drought + heat), and cotton genotypes assigned to the main plots and sub-plots respectively. The results showed that the combined stress had a more severe impact on the yield and fiber quality of cotton genotypes compared to individual stresses. Among the studied genotypes, FB-Shaheen, FH-207, MNH-886, and White Gold exhibited superior performance in regard to agronomic and fiber quality characters under combined stress environments. Physiological parameters, including transpiration rate, stomatal conductance, relative water contents, and photosynthetic rate, were significantly reduced under combined stress. However, specific genotypes, MNH-886, FH-207, White Gold, and FB-Shaheen, demonstrated better maintenance of these parameters, indicating their enhanced tolerance to the combined stress. Furthermore, the accumulation of reactive oxygen species was more pronounced under combined stress compared to individual stressors. Tolerant genotypes showed lower levels of H2O2 and MDA accumulation, while susceptible genotypes exhibited higher levels of oxidative damage. Antioxidant enzyme activities, such as superoxide dismutase, peroxidase, and catalase, increased under combined stress, with tolerant genotypes displaying higher enzyme activities. Conversely, susceptible genotypes (AA-703, KZ 191, IR-6, and S-15) demonstrated lower increases in enzymatic activities under combined stress conditions. Biochemical traits, including proline, total phenolic content, flavonoids, and ascorbic acid, exhibited higher levels in resistant genotypes under combined stress, while sensitive genotypes displayed decreased levels of these traits. Additionally, chlorophyll a & b, and carotenoid levels were notably decreased under combined stress, with tolerant genotypes experiencing a lesser decrease compared to susceptible genotypes.
ABSTRACT
Leafy vegetables like lettuce (Lactuca sativa L.) naturally have high nitrate content and the European Commission has set maximum level for nitrate in lettuce. Glycinebetaine is an organic osmolyte alleviating plant stress, but its role in leaf nitrate accumulation remains unknown. The uptake of glycinebetaine by lettuce roots, and its potential to regulate lettuce nitrate content and improve plant quality were investigated. Two hydroponic lettuce experiments were conducted with different glycinebetaine application rates (Exp1: 0, 1, 7.5, and 15 mM; Exp2: 0, 1 + 1 + 1, 1 + 10, and 4 mM). Plants were analyzed at varying time points. Root application resulted in glycinebetaine uptake and translocation to the leaves. Glycinebetaine concentrations > 7.5 mM reduced leaf nitrate up to 40% and increased leaf dry matter content. Glycinebetaine showed a positive effect on leaf mineral and amino acid composition. Thus, glycinebetaine could be a novel strategy to reduce the nitrate content in hydroponic lettuce.
