Barry McGlasson

Application of two-dimensional gel electrophoresis to detect proteins associated with harvest maturity in stonefruit

Abstract The correct assessment of harvest maturity stage of stonefruit is an important determinant of their quality when they reach the consumer. However, the current indices of ripening used (e.g. skin colour, firmness and soluble solids concentration) vary with cultivar, rootstock, growing conditions and seasonal climatic factors. To develop an index that is independent of environmental factors, total proteins were extracted from fruit and separated by 2D-PAGE. Four proteins (Z1, Z2, Y and X) that were synthesised in fruit a few days before optimum harvest maturity were identified in Japanese-type plums ( Prunus salicina ), peaches and nectarines ( Prunus persica ), and European plums ( Prunus domestica ). These proteins are first expressed a few days before optimum harvest date and their expression increases as the fruit mature. The N-termini of the three most prominent proteins from plums (Z1, Z2 and Y) were sequenced. There appears to be close homology between these proteins and those from a range of species including almond, grape and rubber. It appears that these proteins belong to a family of allergens common to plants whose function may be to confer some form of protection to the plant during periods of stress. These proteins may be used for the development of a test kit that will assist growers to determine optimum harvest maturity for cultivars of plums, peaches and nectarines.

Effects of copper-calcium sprays on fruit cracking in sweet cherry (Prunus avium)

An effective and potentially commercial reduction of cracking in sweet cherries is reported from experiments conducted on five sites over three seasons. The treatment, Cu(OH)2 at 200 g per 1001 plus Ca(OH)2 at 3 kg per 1001 applied at 3 and 6 weeks after full bloom, resulted in a significant and consistent reduction in the proportion of cracked fruit from susceptible cultivars after moderate crack-inducing rainfall. On the three sites where rain-induced cracking occurred, calcium hydroxide was ineffective but copper hydroxide alone, at a low concentration or in combination with calcium hydroxide, significantly reduced fruit cracking. On the remaining two sites cracking of immersed fruit confirmed the field results. The increase in number of intact fruit for the copper hydroxide-calcium hydroxide mixture ranged from 27 to 36% in trials where rain-induced fruit cracking occurred. The treatments were ineffective in controlling cracking during an extended rain period of 12 days.

Root zone temperature influences growth, partitioning, leaf morphology and physiology of the peach rootstock, Green Leaf Nemaguard

This paper examines the hypothesis that root zone temperature (RZT) affects the growth of stone fruit plants. This hypothesis was tested by growing plants of the peach rootstock, Green Leaf Nemaguard (Prunus persica L. Batsch), at a diurnally variable (26/15°C) or at constant (5, 15, 20°C) RZTs; the plants were either actively growing or emerging from dormancy when the treatments were applied. These trials demonstrated that RZT, independently of air temperature and light intensity, influences growth, dry matter partitioning, leaf morphology and physiological processes. The growth of plants emerging from dormancy was more sensitive to RZT than that of actively growing plants, therefore, phenology can influence sensitivity to RZT. The area, numbers and daily rates of expansion of leaves, correlated positively with RZT for both sets of plants. However, plants exposed to a diurnally variable 26/15°C RZT were smaller with respect to overall growth and aspects of leaf morphology than plants exposed to a constant 20°C RZT, despite the daily mean RZTs for both treatments being similar. This could be due to supraoptimal RZTs during the day and/or suboptimal RZTs at night. Root mass ratio, in both actively growing and plants exiting dormancy was highest at 20° RZT. In contrast, the stem mass ratio of actively growing plants was maximised at 5°C, and for plants exiting dormancy, the stem mass ratio was minimised at this RZT. RZTs influence the rate of leaf expansion, which in turn affects the total number of leaves and leaf area and, along with its effect on CO2 assimilation rates, results in reductions in DM production. This research illustrates the importance of RZTs, particularly in the spring, on growth and leaf development and suggests the need to incorporate RZT into development models for peaches.

Changes in ACC and conjugated ACC following controlled atmosphere storage of nectarine

Low temperature disorders of nectarines are thought to be expressions of chilling injury. Chilling injury is a form of stress usually associated with increased synthesis of ethylene and its immediate precursor, aminocyclopropane-1-carboxylic acid (ACC). However, other mechanisms for the development of chilling injury have been proposed. To help determine the nature of the processes leading to chilling injury in nectarines (Prunus persica) and how the gaseous composition of the storage atmosphere effects the development of low temperature disorders, levels of ACC and conjugated ACC were measured in fruit of the cv. Arctic Snow. These compounds were measured in fruit ripened at 20°C immediately after harvest, in fruit on removal from cold storage and in fruit ripened at 20°C following cold storage. During storage, fruit were kept at 0°C in the 4 following atmospheres: air; air + 15% CO2; air + 15 µL/L ethylene; and air + 15% CO2 + 15 µL/L ethylene. Concentrations of ACC remained low in all treatments and no significant changes in ACC levels due to added ethylene or CO2 were observed. Concentrations of conjugated ACC were about 10-times that of ACC and again were not influenced by the composition of the storage atmosphere. No significant changes in either ACC or conjugated ACC were observed until after flesh bleeding, the major symptoms of low temperature disorder expressed in these fruit, had begun to appear. It was concluded that disorders in nectarines stored at low temperatures are not a stress response involving a disruption of ethylene metabolism but may be associated with differential changes in the metabolism of enzymes associated with normal ripening.