Effect of Temperature on Photoreductive Activity of Chloroplasts From Passionfruit Species of Different Chilling Sensitivity

Abstract

The Hill reaction activity of chloroplast membranes isolated from five Passiflora species of different chilling sensitivity was determined as a function of temperature over the range 0 - 40°C. Activity was measured by the photoreduction of ferricyanide in the presence of gramicidin D. In two lowland tropical and chilling-sensitive species, P. quadrangularis and P. edulis forma flavicarpa, the apparent Arrhenius activation energy (Ea) for ferricyanide photoreduction was more than doubled at temperatures below 16 and 10°C, respectively. This increase in Ea was also characteristic of more chilling- resistant species. P. cincinnata, which is intermediate in chilling sensitivity between the two lowland tropical and the other two species studied, showed an increase in Ea below 15°C. A hybrid of this species with P. edulis forma flavicarpa behaved similarly. In chloroplasts from P. edulis, a species relatively resistant to chilling temperatures, there was an increase in Ea below 16°C, like that shown by P. quadrangularis, as well as another increase below 4°C. P. caerulea, the most chilling-resistant of the species studied, showed changes in Ea at 7 and 19°C. Thus, there was no clear correlation between the chilling sensitivity or resistance of a species and the presence or absence of a change in the temperature dependence of the Hill activity at low temperatures. The heat stability of the photoreductive activity of chloroplasts isolated from the various Passiflora species also did not correlate with their chilling sensitivity. The heat stability of photoreductive activity in the most cold-tolerant species, P. caerulea, was comparable with that found for the tropical species, while chloroplasts from P. cincinnata were more heat-labile than chloroplasts from the other species.