Photosynthetic response of in vitro guayule plants in low and high lights and the role of non-photochemical quenching in plant acclimation

Abstract

Guayule (Parthenium argentatum L.) is a hypoallergenic latex-producing rather recalcitrant crop. During in vitro regeneration, the growth and the photosynthetic response of guayule is strongly affected by light intensities. We have used chlorophyll a (Chl-a) fluorescence to study the photosynthetic responses of in vitro grown guayule plants under low light (100μmolm−2s−1) and high light (1250μmolm−2s−1). In high light (HL), the shoot length was reduced and fresh and dry weights were enhanced, contrary to low light (LL) plant response. Total chlorophyll (Chl) and carotenoid contents based on fresh weight or leaf area were reduced by about 50% in HL compared to LL. Although maximum efficiency (Fv/Fm) of photosystem II (PSII) in the dark, electron transport rate (ETR-I), and quantum yield of photosystem I (PSI) were unaffected, the electron transport rate (ETR-II), quantum yield of PSII and non-photochemical quenching (NPQ) were ∼78–88% higher in HL than LL. There were no significant differences observed in malondialdehyde (MDA) content during regeneration of plants in either HL or LL. The higher NPQ in HL grown plants than LL grown plants suggests that NPQ plays an important role in photoprotection during acclimation of guayule plants when exposed to HL.