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Chlorophyll Accumulation and In Vivo Studies on Protochlorophyllide Pool in Wheat Seedlings Grown Under Red Light Photoperiods

Abstract

Wheat seedlings were grown in red light (1500 μmol m^-2 s^-1) for different photoperiods having their root shoot transition zones exposed or covered from red light. Seedlings grown under 2h L, accumulated similar amount of chlorophyll and carotenoids in both the conditions. However, the amount of chlorophyll, carotenoid and protochlorophyllide decreased with increase in photoperiod and increased with increase in photoperiod respectively in seedlings having root shoot transition zones exposed and covered respectively. Low temperature 77k spectra of leaves excised just before the end of dark period from plants showed that a blue shift was observed in the photo-transformable Pchlide with F655 shifting to F653 from 2h to 6h L in seedlings grown with their root-shoot transition zone exposed. This shows the presence of prolamellar bodies in these seedlings. However, in 2hL, photosystem II (PSII) and photosystem I (PSI) were absent in seedlings with their root-shoot transition zones exposed whereas PS I was absent in the seedlings with their root-shoot transition zone covered. Well defined PSI and II were observed in 4hL and 6hL photoperiod in these seedlings. Results demonstrate that a threshold of red light is required for manifestation of present inhibition of greening process and subsequent dark period does not restore the greening process. Synthesis of PORA and subsequent assembly of Pchlide-PORA is also affected as demonstrated by increase in ratio of relative fluoresence of Pchlide to Chlide and by blue shift in the photo transformable Pchlide forms.

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