Fengjuan Lv

Effect of late planting and shading on cellulose synthesis during cotton fiber secondary wall development.

Cotton-rapeseed or cotton-wheat double cropping systems are popular in the Yangtze River Valley and Yellow River Valley of China. Due to the competition of temperature and light resources during the growing season of double cropping system, cotton is generally late-germinating and late-maturing and has to suffer from the coupling of declining temperature and low light especially in the late growth stage. In this study, late planting (LP) and shading were used to fit the coupling stress, and the coupling effect on fiber cellulose synthesis was investigated. Two cotton (Gossypium hirsutum L.) cultivars were grown in the field in 2010 and 2011 at three planting dates (25 April, 25 May and 10 June) each with three shading levels (normal light, declined 20% and 40% PAR). Mean daily minimum temperature was the primary environmental factor affected by LP. The coupling of LP and shading (decreased cellulose content by 7.8%–25.5%) produced more severe impacts on cellulose synthesis than either stress alone, and the effect of LP (decreased cellulose content by 6.7%–20.9%) was greater than shading (decreased cellulose content by 0.7%–5.6%). The coupling of LP and shading hindered the flux from sucrose to cellulose by affecting the activities of related cellulose synthesis enzymes. Fiber cellulose synthase genes expression were delayed under not only LP but shading, and the coupling of LP and shading markedly postponed and even restrained its expression. The decline of sucrose-phosphate synthase activity and its peak delay may cause cellulose synthesis being more sensitive to the coupling stress during the later stage of fiber secondary wall development (38–45 days post-anthesis). The sensitive difference of cellulose synthesis between two cultivars in response to the coupling of LP and shading may be mainly determined by the sensitiveness of invertase, sucrose-phosphate synthase and cellulose synthase.

Effects of different planting dates and low light on cotton fibre length formation

Declining temperature and low light often appear together to affect cotton (Gossypium hirsutum L.) growth and development. To investigate the interaction on fibre elongation, two cultivars were grown in fields in 2010 and 2011 and in pots in 2011 under three shading levels for three planting dates, and the differences of environmental conditions between different planting dates were primarily on temperature. Fibre length in the late planting date 25 May was the longest instead of the normal planting date. Late planting prolonged fibre elongation period and the effect of late planting on fibre length formation was greater than low light. In the normal planting date, shading increased fibre length through delaying the peak of β-1,3-glucanase gene expression and bringing the peak of β-1,3-glucan synthase gene expression forward, leading to a longer duration of plasmodesmata(PD) closure to increase fibre length, instead of changing sucrose contents or relate enzyme activities. However, in the late planting dates, the difference of the duration of PD closure between shading treatments was not obvious, but low light had a negative impact on sucrose contents, sucrose synthase (SuSy) and vacuolar invertase(VIN) activities during fibre rapid elongation period, leading to the decline of fibre length. Due to late planting and low light, the decreased extent of fibre length of Sumian 15 was larger than Kemian 1. Under the combined condition, Sumian 15 had a shorter gene expression of Expansin, and more sensitive sucrose content, VIN and SuSy activity during fibre rapid elongation period. This resulted in the length formation of Sumian 15 which was more sensitive than Kemian 1, when the cotton suffered the combined effects.

Photosynthetic characteristics of the subtending leaf of cotton boll at different fruiting branch nodes and their relationships with lint yield and fiber quality

To investigate photosynthetic characteristics of the subtending leaf at the 2–3rd and 10–11th fruiting branch (FBN, FB2–3, and FB10–11), and their relationship with cotton yield and quality, field experiments were conducted using two cotton cultivars, Kemian 1 and Sumian 15. The results showed that with FBN increasing, chlorophyll (Chl) components, Pn and non-photochemical quenching (NPQ) in the subtending leaf significantly declined, while soluble sugar, amino acid and their ratio (CSS/CAA) as well as Fv/Fm increased. These results indicated that (1) non-radiative dissipation of excess light energy at FB2–3 was reduced to improve solar energy utilization efficiency to compensate for lower Pn, (2) higher NPQ at FB10−11 played a role in leaf photo-damage avoidance, (3) boll weight was related to the CSS/CAA ratio rather than carbohydrates content alone, (4) with FBN increasing, lint biomass and lint/seed ratio increased significantly, but lint yield decreased due to lower relative amount of bolls, and (5) the decreases in Pn, sucrose content and CSS/CAA in the subtending leaf at FB2–3 resulted in lower boll weight and fiber strength.

Photosynthetic characteristics of the subtending leaf and the relationships with lint yield and fiber quality in the late-planted cotton

To investigate the photosynthetic characteristics in the subtending leaf of cotton (Gossypium hirsutum L.) boll (LSCB), and their relationships with lint yield and fiber quality under cool temperature due to late planting, field experiments during 2009 to 2011 were conducted using two different cool temperature-tolerant cultivars, Kemian 1 (temperature-tolerate) and Sumian 15 (temperature-sensitive), at three planting date (25 April, 25 May and 10 June) in Nanjing (118°50′E, 4 32°02′N), China. First, the chlorophyll components in LSCB decreased with days post-anthesis, as well as soluble sugar content, amino acid content and C/N ratio. In addition, Pn, ΦPS II and Fv/Fm significantly decreased, indicating that Pn depression in LSCB was due to non-stomata closure. Second, under cool temperature due to late planting (from 25 April to 25 May and/or 10 June), Pn depression was due to stomata closure. Compared to Sumian 15, Kemian 1 demonstrated superior photosynthetic capacity. Furthermore, under cool temperature, lint biomass and seed biomass significantly decreased in parallel with the lint distribution rate, seed distribution rate and lint/seed ratio, whereas carpel distribution rate increased. These changes under cool temperature led to low lint yield and fiber strength. According to CVs and variance among three planting dates, Sumian 15 was more sensitive to cool temperature than Kemian 1.

The Effects of Fruiting Positions on Cellulose Synthesis and Sucrose Metabolism during Cotton (Gossypium hirsutum L.) Fiber Development

Cotton (Gossypium hirsutum L.) boll positions on a fruiting branch vary in their contribution to yield and fiber quality. Fiber properties are dependent on deposition of cellulose in the fiber cell wall, but information about the enzymatic differences in sucrose metabolism between these fruiting positions is lacking. Therefore, two cotton cultivars with different sensitivities to low temperature were tested in 2010 and 2011 to quantify the effect of fruit positions (FPs) on fiber quality in relation to sucrose content, enzymatic activities and sucrose metabolism. The indices including sucrose content, sucrose transformation rate, cellulose content, and the activities of the key enzymes, sucrose phosphate synthase (SPS), acid invertase (AI) and sucrose synthase (SuSy) which inhibit cellulose synthesis and eventually affect fiber quality traits in cotton fiber, were determined. Results showed that as compared with those of FP1, cellulose content, sucrose content, and sucrose transformation rate of FP3 were all decreased, and the variations of cellulose content and sucrose transformation rate caused by FPs in Sumian 15 were larger than those in Kemian 1. Under FP effect, activities of SPS and AI in sucrose regulation were decreased, while SuSy activity in sucrose degradation was increased. The changes in activities of SuSy and SPS in response to FP effect displayed different and large change ranges between the two cultivars. These results indicate that restrained cellulose synthesis and sucrose metabolism in distal FPs are mainly attributed to the changes in the activities of these enzymes. The difference in fiber quality, cellulose synthesis and sucrose metabolism in response to FPs in fiber cells for the two cotton cultivars was mainly determined by the activities of both SuSy and SPS.

Effect of shading on yield, fiber quality and physiological characteristics of cotton subtending leaves on different fruiting positions

Little is known regarding to impact of simulated shading conditions on cotton yield and fiber quality at different fruiting positions. In this 2-year study, our field experiments investigated the effects of shading percentage on the cotton yield, fiber properties, photosynthesis, and carbohydrate concentrations in boll’s subtending leaves during various growing stages at different fruiting positions (FP). Net photosynthetic rate and effective quantum yield of PSII photochemistry decreased in response to shading on both FP1 and FP3 of the 7th sympodial branches, respectively. Shading also reduced sucrose and starch contents of leaves at each fruiting position. Shading decreased the number and mass of cotton bolls, the fiber strength and micronaire, while the fiber length increased at both fruiting positions. Our results suggested that shading resulted in the reduction of the cotton yield and fiber quality, which are mainly associated with the changes in boll number and alteration of photosynthesis and carbohydrate concentrations during the boll development.