Previous studies have documented cotton boll weight reductions under drought, but the relative importance of the subtending leaf, bracts and capsule wall in driving drought-induced reductions in boll mass has received limited attention. To investigate the role of carbon metabolism in driving organ-specific differences in contribution to boll weight formation, under drought conditions. Controlled experiments were carried out under soil relative water content (SRWC) (75 ± 5)% (well-watered conditions, control), (60 ± 5)% (moderate drought) and (45 ± 5)% (severe drought) in 2018 and 2019 with two cultivars Yuzaomian 9110 and Dexiamian 1. Under severe drought, the decreases of photosynthetic rate (Pn) and carbon isotope composition (δ13C) were observed in the subtending leaf, bract and capsule wall, suggesting that carbon assimilation of three organs was restricted and the limitation was most pronounced in the subtending leaf. Changes in the activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy), invertases as well as the reduction in expression of sucrose transporter (GhSUT1) led to variabilities in the sucrose content of three organs. Moreover, photosynthate distribution from subtending leaf to seeds plus fibers (the components of boll weight) was significantly restricted and the photosynthetic contribution rate of subtending leaf to boll weight was decreased, while contributions of bracts and capsule wall were increased by drought. This, in conjunction with the observed decreases in boll weight, indicated that the subtending leaf was the most sensitive photosynthetic organ to drought and was a dominant driver of boll weight loss under drought. Therefore, the subtending leaf governs boll weight loss under drought due to limitations in carbon assimilation, perturbations in sucrose metabolism and inhibition of sucrose transport.
Abstract The potential mechanisms by which drought restricts cotton fiber cell wall synthesis and fiber strength are still not fully understood. Herein, drought experiments were conducted using two cultivars of upland cotton (Gossypium hirsutum), Dexiamian 1 (drought-tolerant) and Yuzaomian 9110 (drought-sensitive). Results showed that drought notably reduced sucrose efflux from cottonseed coats to fibers by down-regulating the expression of GhSWEET10 and GhSWEET15 in outer cottonseed coats, leading to enhanced sucrose accumulation in cottonseed coats but decreased sucrose accumulation in fibers. Within cotton fibers, drought restricted the hydrolysis of sucrose to uridine-5ʹ-diphosphoglucose by suppressing sucrose synthase activity, and drought favored the conversion of uridine-5ʹ-diphosphoglucose to β-1,3-glucan rather than cellulose by up-regulating GhCALS5. Hence, cellulose content was reduced, which was the main reason for the decreased fiber strength under drought. Moreover, drought promoted lignin synthesis by up-regulating the expression of Gh4CL4, GhPAL9, GhCCR5, GhCAD11, and GhCOMT6, which partly offset the negative influence of reduced cellulose content on fiber strength. Compared with Yuzaomian 9110, the drought-tolerance of Dexiamian 1 was evidenced by the following under drought conditions: (i) greater sucrose flow from seedcoat to fiber, (ii) less β-1,3-glucan accumulation, and (iii) more lignin biosynthesis. Overall, this study provides new insights into the mechanism of reduced cotton fiber strength induced by drought.
Sixteen cotton cultivars widely planted in China were sowed under five different drought concentrations (0, 2.5, 5, 7.5, and 10%) using PEG6000 to screen the indices of drought resistance identification and explore the drought resistance of different cotton cultivars. Eighteen physiological indices including root, stem, and leaf water contents (RWC, SWC, and LWC), net photosynthetic rate (Pn), the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (ϕPSII), non-photochemical quenching coefficient (NPQ), leaf water potential (LWP), osmotic potential (ψs), leaf relative conductivity (REC), leaf proline content (Pro), leaf and root soluble protein contents (LSPC and RSPC), leaf and root malondialdehyde (MDA) contents (LMDA and RMDA), root superoxide dismutase, peroxidase, and catalase activities (RSOD, RPOD, and RCAT) were measured. Results indicated the 18 physiological indices can be converted into five or six independent comprehensive indices by principal component analysis, and nine typical indices (Fv/Fm, SWC, LWP, Pro, LMDA, RSPC, RMDA, RSOD, and RCAT) screened out by a stepwise regression method could be utilized to evaluate the drought resistance. Moreover, the 16 cotton cultivars were divided into four types: drought sensitive, drought weak sensitive, moderate drought resistant, and drought resistant types. The resistance ability of two selected cotton cultivars (drought resistant cultivar, Dexiamian 1; drought sensitive cultivar, Yuzaomian 9110) with contrasting drought sensitivities were further verified by pot experiment. Results showed that the responses of final cotton biomass, yield, and yield composition to drought were significantly different between the two cultivars. In conclusion, drought resistant cultivar Dexiamian 1 and drought sensitive cultivar Yuzaomian 9110 were screened through hydroponics experiment, which can be used as ideal experimental materials to study the mechanism of different cotton cultivars with contrasting drought sensitivities in response to drought stress.
Abstract The formation of cotton fiber strength largely relies on continuous and steady sucrose supply to cellulose synthesis and is greatly impaired by drought. However, the effects of drought on sucrose import into fiber and its involvement in cellulose biosynthesis within fiber remain unclear. To end this, moisture deficiency experiments were conducted using two Gossypium hirsutum cultivars of Dexiamian 1 (drought-tolerant) and Yuzaomian 9110 (drought-sensitive). Fiber strength was significantly decreased under drought. The results of 13 C isotope labeling indicated that drought notably reduced sucrose efflux from cottonseed coat to fiber, and this was caused by down-regulation of sucrose transporter genes ( GhSWEET10 and GhSWEET15 ) in the outer cottonseed coat, finally leading to decreased sucrose accumulation in fiber. Further, under drought, the balance of sucrose allocation within fiber was disrupted by increasing the flow of sucrose into β-1,3-glucan synthesis and lignin synthesis but hindering that into cellulose synthesis in both cultivars. Additionally, glycolysis and starch synthesis were specifically enhanced by drought in Yuzaomian 9110, which further reduced the flow of sucrose into cellulose synthesis. Under drought, the cellulose deposition was decreased due to promoted cellulose degrading process in Dexiamian 1 and stunted cellulose synthesis in Yuzaomian 9110. Consequently, reduced cellulose content was measured in drought-stressed fibers for both cultivars. In summary, the inhibited cellulose accumulation caused by drought was mainly due to reduced sucrose translocation from the outer cottonseed coat to fiber, and less sucrose partitioned to cellulose synthesis pathway under the condition of intensified competition for sucrose by different metabolic pathways within fiber, finally degrading the fiber strength. Highlight This article revealed the path of sucrose flow from cottonseed coat to cotton fiber and sucrose competition patterns within cotton fiber under drought and their relationships with fiber strength loss.
The bulbs of the lily plant Fritillaria thunbergii Miq. possess substantial medicinal properties for relieving coughs and clearing the lungs. However, excessive pursuit of yield during cultivation has led to a decrease in medicinal ingredients. Therefore, we aimed to investigate the effects of two single-factor treatments, shading (SK0) and potassium application (S0K), and their coupling treatment (SK) on bulb biomass and medicinal substance content, along with the role of rhizosphere microorganisms. Shading increased the content of active ingredients in bulbs by approximately 11.7% while decreasing bulb biomass by approximately 11.3%. SK treatment mitigated the biomass reduction caused by SK0 treatment while enhancing the accumulation of active ingredients in F. thunbergii, up to 1.2 times higher than that of SK0 treatment. In rhizosphere soil, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium (ANPR), Chryseobacterium, Brevundimonas, and Phoma exhibited significant positive correlations with medicinal components, among which ANPR, Brevundimonas, Chryseobacterium, and Phoma were responsive to SK treatments. Also, Burkholderia-Caballeronia-Paraburkholderia (BCP) and Brevundimonas responded to changes at different growth stages of F. thunbergii. The relative abundance of these microorganisms was associated with the alterations of soil factors resulting from shading or K application. Our results indicate that these microorganisms are beneficial to the growth of bulbs and the synthesis of active components in F. thunbergii. The combination of shading and K application may regulate the accumulation of medicinal substances in F. thunbergii by modulating the structure of the soil microbial community. Our results serve as a reference for soil improvement for medicinal plant cultivation.
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