Photoinhibition of photosynthesis in mango leaves: effect of chilly nights.
Nir G., Ratner K., Gussakovsky E. E., Shahak Y.
Author Affiliation: Jordan Valley R&D Authority, MP Hevel Jericho 91906, Israel.
: 228-235
Abstract : Excessive light radiation being absorbed by leaves can result in inactivation and/or impairment of the chlorophyll-containing reaction centres of the chloroplasts, and cause photoinhibition of photosynthesis (PI, light stress). The susceptibility of leaves to photoinhibition can be increased by other stress factors which coincide with the light. The effects of cold temperatures on mango cv. Sabre (2-4 years old) and mango rootstock 13/1 (in 10-litre pots containing a 1:1:1 mixture of tuff:peat moss:sandy loam) prior to light exposure were investigated in Israel. The plants were kept in a greenhouse (30/18°C, day/night) during winter and spring, and in 50% shade outside for the rest of the year. Cold nights increased photodamage which developed in sun-exposed leaves the following day. Photoinhibition was monitored by the decrease in photosystem II quantum efficiency, as detected by the chlorophyll fluorescence parameter Fv/Fm, and by gas exchange. The effects of cold nights were expressed in sun-exposed, but not in shaded leaves. The daily PI which developed after warm nights was fully reversible, and after cold nights it was irreversible. Photoinhibition damage gradually accumulated during repeated cycles of cold nights and sunny days. Cold nights reduced CO2 uptake capacity and stomatal conductance. The cold night effect on PI occurs readily in subtropical/tropical trees such as mango and papaya, to a lesser extent in citrus, and does not occur in peach leaves.