Effect of light and gibberellic acid on photosynthesis during leaf senescence of alstroemeria cut flowers.

Abstract

The functioning of the photosynthetic apparatus during leaf senescence was investigated in alstroemeria cut flowers by a combination of gas‐exchange measurements and analysis of in vivo chlorophyll fluorescence. Chlorophyll loss in leaves of alstroemeria cut flowers is delayed by light and by a treatment of the cut flowers with gibberellic acid (GA3). The maximal photosynthesis of the leaves was approximately 6 μmol CO2 m−2 s−1 at I 350 μmol m−2 s−1 (PAR) which is relatively low for intact C3 leaves. Qualitatively the gas‐exchange rates followed the decline in chlorophyll content for the various treatments, i.e. light and GA3‐treatment delayed the decline in photosynthetic rates. However, when chlorophyll loss could not yet be observed in the leaves, photosynthetic rates were already strongly decreased. In vivo fluorescence measurements revealed that the decrease in CO2 uptake is (partly) due to a decreased electron flow through photosystem II. Furthermore, analysis of the fluorescence data showed a high nonphotochemical quenching under all experimental conditions, indicating that the consumption of reducing power in the Calvin cycle is very low. The chlorophyll, remaining after 9 days incubation of leaves with GA3 in the dark should be considered as a ‘cosmetic’ pigment without any function in the supply of assimilates to the flowers.