The Physiology of Growth in Apple Fruits IV. Seasonal Variation in Cell Size, Nitrogen Metabolism, and Respiration in Developing Granny Smith Apple Fruits

Abstract

Results of investigation of cell size, fruit size, nitrogen metabolism, and respiration rate over three successive seasons confirm the main conclusions of earlier papers in this series. Fruit left on the trees for a period beyond normal commercial maturity showed a very -large increase in soluble nitrogen with only slight increase in protein nitrogen. The relation of the nitrogen and organic acid metabolism to the climacteric rise in respiration is discussed.

Effect of Blossom Density and Crop Load on Growth, Fruit Quality, and Return Bloom in ‘Honeycrisp’ Apple

“…Fruit size is determined by cell number, cell size, and intercellular space (Goffinet et al, 1995). However, cell number, which is determined early in apple development, accounts for most of the variation in fruit size (Pearson and Robertson, 1953), and it can be influenced by the previous year's crop load and may reduce the number of cells in the flower receptacles if it is excessive (Bergh, 1985). Therefore, the destined size of an apple may be determined by the current as well as previous year resources.…”

The Physiology of Growth in Apple Fruits VI. the Control of Respiration Rate and Synthesis

“…It has been shown in earlier work on fruit from some of the same trees (Robertson and Turner 1951;Pearson and Robertson 1953) that a number of changes took place in the cells prior to and during the climacteric rise (Fig. 8).…”

“…The breakdown of starch which is taking place concurrently in these fruits will contribute a phosphorylated hexose to enter the respiration system and hence act as a source of substrate in the cytoplasm, so that substrate supply is less likely to become limiting. In this connection, it is important to note that the loss of starch between 185 and 225 days (see Pearson and Robertson 1953) is about 8 X 10-8 g per cell or 0.2 X 10-8 g per cell per day. If all this starch were respired as phosphorylated hexose it would produce 1.4 X 10-7 mg CO2/cell/hr, and as the respiration rate at 225 days is 1.2 X 10--: 7 mg CO2!hr, the hexose from starch would account approximately for the increase in respiration rate.…”

“…The utilization of succinate, citrate, and malate by these particles provides evidence for the possible participation of a tricarboxylic acid cycle . (Pearson and Robertson 1953) to show the relationS in time between the changes in starch, protein and soluble nitrogen, organic acids, and respiration rate.…”

“…This is inversely related to the ATP / ADP ratio at a constant concentration of adenosine polyphosphat e. The respiration rate will be low when this ratio is high because the ADP con-centration will then be low, and will increase, with increase in the ADP to accept phosphate, when this ratio falls. It has been suggested (Pearson and Robertson 1953) that the sharp increase in respiration rate (Fig. 8) at about 190 days from blossom is due to the increase in ADP relative to ATP when the maintenance of protein and other unstable compounds already synthesized makes high demands on the energy-carrying system.…”