Carbohydrate Accumulation in the Cotton Plant at Low Moisture Levels

114

Two photoperiodic cotton (Gossypium hirsutum L.) strains (T185 and T466) which had been empirically selected because of poor performance and two strains (T25 and T256) selected because of enhanced performance under field water stress were evaluated for stress-induced changes in their organic acids and carbohydrates. Profiles and quantitation of organic acids and carbohydrates from aqueous extractions of cotton leaf tissue were determined by high performance liquid chromatography. In all cases, the water-stressed plants showed two to five times greater amounts of organic acids and carbohydrates over the values determined for the irrigated samples. Under stress, sucrose accumulation was observed in wilting strains (poor performers) probably related to rate of translocation out of the leaf. The most dramatic response to water stress was the accumulation of citric acid in strains T25 and T256 as compared to T185 and T466. Citric/malic acid ratios for both the irrigated and waterstressed samples of T25 and T256 were twice those of T185 and T466.Organic acids and carbohydrates have been implicated in various roles in the metabolic and physiological responses of plants to water stress. Early papers by reported that, at low water levels, carbohydrates accumulated in cotton plants which had complete fruit loads. In cotton leaves, drought caused large reductions in starch concentrations, variable effects on sucrose, and an increase in hexose sugar. The gains in sugars were substantial on a relative basis but were minor in actual amounts. They concluded that drought appears to depress carbohydrate utilization by the cotton plant to a greater extent than it does photosynthesis (7).Malic, citric, and oxalic acids are frequently found in large amounts (several percent of the dry weight of the tissue) in mature tissues or organs of plants (4). For cotton, higher concentrations of organic acids are found in the leaves than in other vegetative parts, frequently at 10% of the basis of dry weight (8). The major acids accounting for a total content of approximately 10% of the dry weight of cotton leaves were identified as citric, malic, and oxalic, with malic usually present in the greatest amount. It was reported that drought caused large reductions in concentrations of citric acid with gains in malic acid but with overall maintenance of the level oftotal organic acids (8

mentioning

confidence: 99%

“…The gains in sugars were substantial on a relative basis but were minor in actual amounts. They concluded that drought appears to depress carbohydrate utilization by the cotton plant to a greater extent than it does photosynthesis (7).…”

mentioning

confidence: 99%

Effects of Water Stress on the Organic Acid and Carbohydrate Compositions of Cotton Plants

Timpa¹,

Burke²,

Quisenberry³

et al. 1986

114

“…in the absence of wilting, the advantages of the higher carbohydrate le-,Tels on boll and fiber development may more than offset the disadvantages of reduced moisture supply. In bolls of these two varieties, 13 days old, the percentage of moisture was reduced 2 and 1% in the drouth treatment and 1 and 07% in the two-boll treatment. These samples (a total of 72 bolls for each treatment and variety) were collected during midmorning and mid-afternoon on six days.…”

Section: Discussionmentioning

confidence: 87%

Fiber Properties and Carbohydrate and Nitrogen Levels of Cotton Plants as Influenced by Moisture Supply and Fruitfulness

Eaton

Ergle

1952

Self Cite

As distinct from the cereal crops and the spring-flowering fruits, which are characterized by a reproductive climax, cotton is like the tomato and cucurbits in its indeterminate growth; but it is different in the minor extent to which fruit size is influenced by environment and fruitfulness. In a regional variety study (3), 16 varieties of cotton planted during each of three years at eight locations showed locational variations in the varietal means of only 8%c in fiber length, 6%c in fiber weight-per-inch and 9%0 in fiber strength. In terms of use value, however, such differences have high significance. The tendency toward uniformity in the bolls of cotton is accounted for by the extent to which young bolls are shed as the plant becomes heavily fruited. Within varieties and environments, the number of developing bolls per unit of vegetative weight (11) has been found to be remarkably uniform.From California irrigation experiments, ADAMS et al.(1) record that reductions in water supply result generally in losses in staple length (usually within 1/32 inch), seed index (usually within 1.0 gram) and lint index (usually within 0.5 gram). Drought has been observed to decrease the length of cotton lint (2, 5, 18); with this effect, an increase in fiber strength was usually found. BERKLEY et al. (4), as well as others, have associated the increased strength of fibers with a narrowing of the angle of the cellulose crystallites (x-ray angles).Increased nitrogen supply has been found to result in some increase in length of fiber (7,16,19). On the other hand, little effect upon length was found by STURKIE (18), whereas, in the presence of inadequate supplies of some other elements, BROWN (6) reported length reductions to result from nitrogenous fertilizers. As has been the general experience with other plants, WADLEIGH (19) found increased nitrogen supply to result in lower carbohydrate accumulations. He associated as causal the plus and minus changes in carbohydrate or nitrogen with the changes in boll properties and in fiber length that corresponded in sign.CROWTHER (7) and NELSON (16) have shown phosphate to increase boll size but not to alter fiber properties. Nelson also found that potash additions which greatly increased yield also increased fiber length and weight per inch; the x-ray angles were increased and the strength of fiber and yarn decreased. YOUNGE (20) has shown sulphur deficiency that reduced boll production had little effect on fiber properties.

“…The level of cotton leaf starch required to continue nocturnal carbon export at daytime rates is less than that normally found in nonstressed field-grown cotton (20) but water stress decreases starch levels in cotton leaves (4,20) provided other stress factors do not interfere (1,2). Severe water stress depresses the starch content of cotton leaves (4) to such an extent that carbon export from them should be largely limited to daylight hours.…”

Section: Discussionmentioning

confidence: 97%

“…Severe water stress depresses the starch content of cotton leaves (4) to such an extent that carbon export from them should be largely limited to daylight hours. Water-stressed plants (19) may therefore exhibit diminished nocturnal leaf export which could lead to a decrease in fruit set (13) and root growth (3,5 …”

Section: Discussionmentioning

confidence: 99%

Carbon Partitioning and Export from Mature Cotton Leaves

Hendrix¹,

Grange²

1991

The partitioning of carbon in intact, mature cotton (Gossypium hirsutum L.) leaves was examined by steady-state 14CO2 labeling.Plants were exposed to dark periods of varying lengths, followed by similar illuminated labeling periods. These treatments produced leaves with a range of starch and soluble sugar contents, carbon exchange, and carbon export rates. Export during the illuminated periods was neither highly correlated with photosynthesis nor was export during the illuminated periods significantly different among the treatments. In contrast, the rate of subsequent nocturnal carbon export from these leaves varied widely and was found to be highly correlated with leaf starch content at the end of the illumination period (r = 0.934) and with noctumal leaf respiration (r = 0.954). Leaves which had accumulated the highest levels of starch (about 275 micrograms per square centimeter) by the end of the illumination period exhibited nocturnal export rates very similar to those during the daylight hours.