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Background: Root system architecture (RSA) exhibits significant genetic variability and is closely associated with drought tolerance. However, the evaluation of drought-tolerant cotton cultivars based on RSA in the field conditions is still underexplored. Results: So, this study conducted a comprehensive analysis of drought tolerance based on physiological and morphological traits (i.e., aboveground and RSA, and yield) within a rain-out shelter, with two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content). The results showed that principal component analysis identified six principal components, including highlighting the importance of root traits and canopy parameters in influencing drought tolerance. Moreover, the systematic cluster analysis was used to classify 80 cultivars into 5 categories, including drought-tolerant cultivars, relatively drought-tolerant cultivars, intermediate cultivars, relatively drought-sensitive cultivars, and drought-sensitive cultivars. Further validation of the drought tolerance index showed that the yield drought tolerance index and biomass drought tolerance index of the drought-tolerant cultivars were 8.97 and 5.05 times higher than those of the drought-sensitive cultivars, respectively. Conclusions: The RSA of drought-tolerant cultivars was characterised by a significant increase in average length-all lateral roots, a significant decrease in average lateral root emergence angle and a moderate root/shoot ratio. In contrast, the drought-sensitive cultivars showed a significant decrease in average length-all lateral roots and a significant increase in both average lateral root emergence angle and root/shoot ratio. It is therefore more comprehensive and accurate to assess field crop drought tolerance by considering root performance. [ABSTRACT FROM AUTHOR]

Leaf senescence reduces the photosynthetic capacity of leaves, thus significantly affecting the growth, development, and yield formation of cotton. Melatonin (MT) is a multipotent substance proven to delay leaf senescence. However, its potential mechanism in delaying leaf senescence induced by abiotic stress remains unclear. This study aimed to explore the effect of MT on delaying drought-induced leaf senescence in cotton seedlings and to clarify its morphological and physiological mechanisms. Drought stress upregulated the leaf senescence marker genes, destroyed the photosystem, and led to excessive accumulation of reactive oxygen species (ROS, e.g., H2O2 and O2−), thus accelerating leaf senescence. However, leaf senescence was significantly delayed when 100 μM MT was sprayed on the leaves of the cotton seedlings. The delay was embodied by the increased chlorophyll content, photosynthetic capacity, and antioxidant enzyme activities, as well as decreased H2O2, O2−, and abscisic acid (ABA) contents by 34.44%, 37.68%, and 29.32%, respectively. MT significantly down-regulated chlorophyll degradation-related genes and senescence marker genes (GhNAC12 and GhWRKY27/71). In addition, MT reduced the chloroplast damage caused by drought-induced leaf senescence and maintained the integrity of the chloroplast lamellae structure under drought stress. The findings of this study collectively suggest that MT can effectively enhance the antioxidant enzyme system, improve photosynthetic efficiency, reduce chlorophyll degradation and ROS accumulation, and inhibit ABA synthesis, thereby delaying drought-induced leaf senescence in cotton. [ABSTRACT FROM AUTHOR]

ABSTRACT The root cortical senescence (RCS) is closely associated with root absorptive function. However, characteristics and responses of RCS to drought stress in cotton have received little attention. This study subjected the drought‐tolerant variety ‘Guoxin 02’ and the drought‐sensitive variety ‘Ji 228’ to drought stress (8% PEG6000) and no‐stress (0% PEG6000) treatments to determine the characteristics and responses of cotton RCS to drought stress. The results showed that the greater the distance from the root tip, the more severe the RCS occurrence under drought stress compared with non‐stress treatment. The occurrence of RCS in ‘Guoxin 02’ increased by 14.03%−20.18% compared to ‘Ji 228’ under drought stress. The RCS was negatively correlated with root respiration but positively correlated with root length and leaf water potential. The silencing of RCS‐related genes (GhSAG12 and GhbHLH121) can mitigate the drought‐induced RCS phenomenon in cotton; however, reduced drought tolerance. Exogenous abscisic acid (ABA) treatment can promote RCS generation. Conversely, ABA synthesis exhibits contrasting effects. In summary, endogenous hormones regulated RCS, which reduced the root metabolic and seemingly achieved more resource redistribution to new roots, thereby fully utilize deep water resources. Thus, the study demonstrates the potential of RCS in improving the drought stress tolerance of cotton. [ABSTRACT FROM AUTHOR]

Background: Cotton (Gossypium hirsutum L.) is one of the most important cash crops worldwide. Fine roots are the central part of the root system that contributes to plant water and nutrient uptake. However, the mechanisms underlying the response of cotton fine roots to soil drought remains unclear. To elucidate the proteomic changes in fine roots of cotton plants under drought stress, 70–75% and 40–45% soil relative water content treatments were imposed on control (CK) and drought stress (DS) groups, respectively. Then, tandem mass tags (TMT) technology was used to determine the proteome profiles of fine root tissue samples. Results: Drought significantly decreased the value of average root diameter of cotton seedlings, whereas the total root length and the activities of antioxidases were increased. To study the molecular mechanisms underlying drought response further, the proteome differences between tissues under CK and DS treatments were compared pairwise at 0, 30, and 45 DAD (days after drought stress). In total, 118 differentially expressed proteins (DEPs) were up-regulated and 105 were down-regulated in the 'DS30 versus CK30' comparison; 662 DEPs were up-regulated, and 611 were down-regulated in the 'DS45 versus CK45' comparison. The functions of these DEPs were classified according to their pathways. Under early stage drought (30 DAD), some DEPs involved in the 'Cutin, suberin, and wax synthesis' pathway were up-regulated, while the down-regulated DEPs were mainly enriched within the 'Monoterpenoid biosynthesis' pathway. Forty-five days of soil drought had a greater impact on DEPs involved in metabolism. Many proteins involving 'Carbohydrate metabolism,' 'Energy metabolism,' 'Fatty acid metabolism,' 'Amino acid metabolism,' and 'Secondary metabolite biosynthesis' were identified as DEPs. Additionally, proteins related to ion transport, stress/defense, and phytohormones were also shown to play roles in determining the fine root growth of cotton plants under drought stress. Conclusions: Our study identified potential biological pathways and drought-responsive proteins related to stress/defense responses and plant hormone metabolism under drought stress. Collectively, our results provide new insights for further improving drought tolerance in cotton and other crops. [ABSTRACT FROM AUTHOR]

Root system architecture (RSA) plays an important role in soil water uptake and plant growth. However, there is a lack of understanding regarding the connection between the changes in RSA characteristics under drought stress in cotton plants and their drought tolerance and yield. This study aims to evaluate the RSA variations in different drought-tolerant cotton cultivars under drought stress, and to assess the correlation between RSA, drought tolerance, and yield. Three drought-tolerant cotton cultivars and three drought-sensitive cotton cultivars were grown in a field equipped with rain shelters to prevent interference from rainfall. Drought stress was initiated at the three-leaf stage, maintaining the soil relative water content at 50 ± 5%, while control plants were irrigated normally at 75 ± 5% soil water content. Multiple parameters, including leaf water potential, relative water content, seed cotton yield, and RSA traits, were assessed. Notable variations in drought tolerance were observed among different cultivars when exposed to drought stress. Specifically, drought-tolerant cultivars exhibited a 34% increase in the average length of all lateral roots and a 15% increase in maximum root depth under drought stress. In contrast, seed cotton yield experienced a reduction of 22.34% in such conditions. Interestingly, there were significant differences in several RSA traits under drought stress, which were not evident under well-watered. Leaf water potential and relative water content were positively correlated with specific root length, dry root weight, average length of all lateral roots and maximum depth, and negatively correlated with average lateral root emergence angle and width/depth ratio. These results underscore the close association between RSA traits and plant drought tolerance. There was also a strong correlation between the seed cotton yield and RSA traits. Specifically, seed cotton yield increased linearly with specific root length, average lengths of lateral roots, and maximum depth, but decreased linearly with root tissue density, and average lateral root emergence angle and width/depth ratio. Optimizing RSA improves drought tolerance and reduces yield loss in drought-tolerant cotton cultivars. Understanding of the role of RSA in plant adaptation to drought stress is important for selecting and developing high-yielding cultivars with superior drought tolerance. This knowledge holds great significance in improving cotton resilience and facilitating adapting to abiotic stress through genetic improvement or agronomic measures. • Genotypic variation in root system architecture (RSA) was revealed under drought. • Root system architecture plays important roles in cotton drought tolerance. • There is a significant coefficient of variation in RSA under drought. • Optimizing RSA can improve cotton drought tolerance and minimize yield loss under drought.. [ABSTRACT FROM AUTHOR]

Drought stress is the major environmental factor that inhibits the growth and reduces the yield of cotton (Gossypium hirsutum L.). The exogenous application of melatonin has been shown to alleviate drought stress damage, but it is unclear whether melatonin mediates the alleviation by preventing the drought-induced inhibition of root growth. To address this gap, we subjected cotton plants grown in RhizoPotsto treatments of thorough watering, drought stress treatment, and drought stress supplemented with exogenous melatonin. Melatonin promoted the aboveground growth compared with the non-melatonin treatment under drought stress, and increased the plant height, stem diameter, leaf area, SPAD value, and net photosynthetic rate. The application of melatonin significantly prevented the drought-induced yield losses by increasing the boll weight. The drought stress+melatonin treatment significantly increased the root length, root surface area, root volume, and specific root length by 18.36%, 25.46%, 26.07%, and 18.53%, respectively, compared with the drought stress treatment. Under drought stress, melatonin increased the root length by increasing its maximum and average rates of accumulation and increased the taproot diameter by increasing its maximum and average rates of accumulation. The drought stress+melatonin treatment significantly increased the lifespan of lateral roots and root hairs compared with the drought stress treatment. In conclusion, this study indicated that exogenous melatonin could improve the drought resistance and yield of cotton by promoting root growth and delaying root senescence. [Display omitted] • Exogenous melatonin enhances cotton drought resistance by promoting root's development and prolonging root's lifespan. • Exogenous melatonin increases the root length by increasing its maximum and average accumulation rates. • Exogenous melatonin increases the length and lifespan of root hairs under drought stress. [ABSTRACT FROM AUTHOR]