Ethnobotanical Leaflets 12: 318-319. 2008.
Effect of High Irradiance on an Ethnobotanically Important Plant (Luffa acutangula Roxb.)
Jegan, G., Parimala, P., Prabhu Inbaraj, M. and Muthuchelian, K.
Centre for Biodiversity and
Luffa acutangula Roxb was examined for the effects of photoinhibition. Our results show that this species is not immune to high irradiance.
Key Words: High irradiance, variable fluorescence, Fv/Fm.ss.
Luffa actuangula Roxb. is cultivated
Photoinhibition is the light-induced reduction in the function of photosystem II (PS II) with an associated decline in quantum efficiency. Photoinhibition may result from direct photodamage to reaction centers or an increase in photo protective mechanisms that deflect excess energy away from PS II. Controlled dissipation of the excess energy prevents damage to the photosynthetic apparatus
When dark-adapted leaves are suddenly subjected to high irradiance, the initial fluorescence, Fo, is the quantity of fluorescence produced when all PS II reaction centres are open. With the absorption of quanta, reaction centres start to close and the maximum fluorescence, Fm, is measured under saturating irradiance when all of the reaction centres are closed. Variable fluorescence Fv is the difference between Fo and Fm. The ratio of Fv and Fm is the intrinsic efficiency of PS II, and obtains an average maximum value of 0.80 – 0.83 for a wide variety of plants growing under optimal conditions (Demmig and Bjorkman 1987). Plant physiologists use measures of fluorescence as an indicator of chlorophyll stress specifically in relation to photosystem II. Greater fluorescence results when photosystem II (PS II) reaction centers are closed or damaged and can no longer accept additional electrons, thus interrupting electron transport. The relationship between chlorophyll and carotenoid may be used as potential indicator of photo-oxidative damages caused by strong irradiation.
Dark-adapted Fv/Fm measurements were taken with the help of Opti-Sciences modulated flourometer OS- 30P (Opti Sciences, Hudson). The fully expanded leaves of Luffa actuangula were exposed to high irradiance for 30 mins. Prior to that chlorophyll fluorescence was measured. After the high irradiance and after 30 minutes of recovery time, the chlorophyll fluorescence was again measured.
Table 1 shows the results of chlorophyll fluorescence of Luffa actuangula. The Fv/Fm value was high (0.914) before high irradiance. After the HI Fv/Fm value was decreased, it showed a slight increase after recovery. Before the HI Fo value was low, but it increased after HI and it decreased after recovery. Variable fluorescence was high before HI and it decreases both after HI and after recovery. Our results are in line with that found by others.
Table 1: Chlorophyll fluorescence value of Luffa actuangula
We are thankful to UGC for their financial support.
Bjorkman, O. and Demmig, B. 1987. Photon yield of O2 evolution and chlorophyll fluorescence characteristics at 77-K among vascular plants of diverse origins. Planta 170: 489-4-504.