TOMATO (LYCOPERSICON-ESCULENTUM MILL, CV BETTER BUSH) PLANT-RESPONSE TO ROOT RESTRICTION .2. ROOT RESPIRATION AND ETHYLENE GENERATION

Our earlier observations of root-restricted tomato plants indicated that alterations in plant morphology occurred from day 18 to 32 of a 46 d culture period. Here, root-respiration capacity and root-ethylene production were measured to determine if these parameters were correlated with the observed changes in plant morphology. Plants were cultured in a flow-through hydroponic system. Roots in large containers (1500 cm3, control), exhibited a gradual decline in respiration capacities, from 9009 to 2147 mm3 O2 g-1 (DW) h-1. A significant decline in respiration capacity was observed for roots grown in small containers (25 cm3, root-restriction treatment) after 18 d in culture. Once treated root systems attained a maximum weight (c. 1.59 g DW), their respiration capacity remained relatively constant (c. 1212 mm3 O2 g-1 (DW) h-1). The observed change in root respiration, for the restricted plants, was closely correlated with alterations in root: shoot ratio. We conclude that the decline in root-respiration capacity represents a significant indicator of reduced root metabolism. Thus, root energetics plays a role that influences the growth habit of root-restricted plants. Slight increases in ethylene production were observed for treated roots on days 22, 25 and 30. This increase in production appeared at a time when adventitious rooting was initiated. Overall, control and treated roots produced ethylene within a range of 6.1 to 10.2 mm3 kg-1 (FW) h-1. Preliminary sampling of leaf tissues suggests that ethylene production rates did not differ for mature leaves of the two plant groups.