SummarySugar levels in the various species of the Saccharum complex suggest an evolutionary increase in sugar content. Under suitable ecological conditions, survival through sucker growth may be dependent on rapid mobilization of stored carbohydrate. Selection pressure for sucrose storage would then oocur if sucrose was more readily remobilized than other storage carbohydrates. It is suggested that this ecological situation occurred in New Guinea, and that natural and not human selection lead to the evolution of S. oJJicinarum.The relationships between total sugars, moisture content, and fibre content indicate that there is an apparent physiological limit to sugar accumulation in the genus Saccharum at about 27% of the fresh weight.
Independent and interaction effects of day and night temperature, photo-period duration, and diurnal thermoperiodicity were studied on sugar-cane grown under controlled environments. During the first 3 months of growth, day and night temperature effects were mainly additive, but at 6 months the interaction effects of all variables were numerous and complex. Many of the interaction effects could be attributed to increased responses to constant-temperature regimes with a 12-hr photoperiod. No evidence for thermoperiodicity requirements was found.
SummaryPhotosynthesis in sugar-cane was linearly related to light intensity up to full sunlight when leaf geometry was similar to that of field-grown plants_ Individual leaves orientated at right angles to the incident radiation were saturated at about two-thirds full sunlight irrespective of whether the leaves developed in low or high light intensities.On a short-term basis, the QlO for photosynthesis was 1·1 over the range 8-34°C. Exposure of intact plants to a 17/10°C day and night temperature regime for a prolonged period resulted in cessation of stalk elongation and an initial rise in stored sugar followed by a decline in photosynthetic efficiency, which was slowly reversible when the temperature was raised_ Photosynthetic efficiency appears to be llD.ked to availability of sinks but may also' be altered by metabolic imbalance induced by environmental shock. End product repression of photosynthesis by sugars was not the operative control in detached leaves exposed toJong light treatments.
3-Indolylacetic acid (IAA) was found to promote the binding of pectin methylesterase (PME) to a cell wall fraction prepared from tobacco pith, the effect being increased by increasing concentration of IAA to a peak of activity, after which inhibition occurred.
SummaryIt is shown that the plant auxins 3·indolylacetic acid, 2,4-dichlorophenoxyacetic acid, and a·naphthalene acetic acid are effective in binding pectin methylesterase (PME) to cell wall preparations from tobacco pith and tubers of the Jerusalem artichoke.Each auxin has an optimum concentration for activity. The activity curves are consistent with the hypothesis that the auxin binds PME to cell wall receptor sites by an adsorption mechanism which can be described by the Langmuir adsorption isotherm.It is suggested that the auxin· mediated binding ofPME could control extension growth by controlling the extent of esterification of the pectic substances of the cell wall.
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