Both the fresh weight and dry weigh increase of peach fruit [Prunus persica (L.) Batsch. cv. Golden Queen] have a double-sigmoid pattern. However, the lag period of slow fresh weight increase (fresh- weight-stage II) began and finished 1 month earlier than the start and finish respectively of the lag period of dry weight increase (dry-weight-stage II). Similarly, after the fruit had matured the rate of fresh weight increase declined 1 week before the rate of dry weight increase declined.
The stone increased in dry weight rapidly in fresh-weight-stage II and this was accompanied by a compensating decline in the rate of dry weight increase of the flesh. There was no rapid increase in the dry weight of the seed until the rate of dry weight increase of the stone declined at the beginning of dry-weight-stage II. Although the decrease in the growth rate of the stone was accompanied by a marked increase in soluble sugar in the flesh, there was no compensating increase in growth rate of the flesh.
While the second rapid stage of fresh weight increase (fresh-weight-stage III) was not accompanied by other apparent physiological changes, the second rapid stage of dry weight increase began at the same time as ripening commenced. The rate of natural abscission and the rate at which chlorophyll was degraded, both of which are known to indicate the level of ethylene present in the tissue, were high in dry-weight-stage I and dry-weight-stage III and low in dry-weight-stage II. The rate of growth of the fruit and its parts during different stages, the growth of the seed, the rate of abscission and chlorophyll degradation and the level of the major metabolites present in the fruit were all intricately interrelated.
We have discussed the physiological significance of these observations and the way in which they may relate to earlier studies of peach fruit growth.
Root competition (tree density), summer pruning, and regulated irrigation were studied to determine whether they can be used to control tree vigor and productivity in ultra-dense orchards of peach [Prunus persica (L.) Batsch]. All methods appeared to inhibit tree growth, but regulated irrigation combined with root competition generated from high tree density was most effective. Fruit yields and fruit growth were significantly increased (up to 30%) by high tree density combined with low rate of water application when water stress limited shoot growth but stimulated subsequent fruit growth. Periods of low rate of water application are specified.
The relationship between L-phenylalanine ammonia-lyase (PAL) activity and anthocyanin synthesis in apple skin was investigated. Enzyme activity was induced by exposure to white light. After a lag phase of less than 10 h, PAL activity increased to a maximum at 30 h and then declined. Anthocyanin accumuIation, after a lag phase of 20 h, continued at a constant rate for a further 100 h.
The increased rate of anthocyanin accumulation which resulted from u.v. light and cycloheximide treatment of whole fruit was preceded by comparable increases in the level of PAL activity. Wounding, which stimulated anthocyanin synthesis in skin discs, caused a far greater increase in PAL activity. In wounded tissue (skin discs) neither u.v. light or cycloheximide treatment caused any increase in anthocyanin accumulation or PAL activity. Cycloheximide inhibited anthocyanin formation in skin discs and, to a lesser extent, reduced PAL activity. When cycloheximide was applied as a single drop to a whole fruit, it inhibited anthocyanin formation but increased PAL activity in the skin to which it was applied. In a surrounding ring of skin, both anthocyanin level and PAL activity were increased.
Without light, anthocyanin synthesis did not occur and there was virtually no PAL activity in whole fruit skin. However, in skin discs held in the dark, PAL activity developed to the same level as in illuminated discs, but no anthocyanin accumulated.
The results indicate that, although the level of PAL activity may control the rate of anthocyanin synthesis in whole fruit, it is not the only critical enzyme regulating anthocyanin synthesis in apple skin. The mechanisms by which treatments may stimulate PAL activity and anthocyanin synthesis and the possible involvement of ethylene are discussed.
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