Effects of light intensity on leaf photosynthetic characteristics, chloroplast structure, and alkaloid content of Mahonia bodinieri (Gagnep. Laferr.
The variation of light intensity has obvious effects on leaf external morphology, internal anatomy, and physiological characteristics; it even induces changes in secondary metabolite production. The effects of different irradiance levels on biomass, gas exchange parameters, and photosynthetic pigment contents in Mahonia bodinieri (Gagnep. Laferr. were analyzed here. Combined analyses of physiology, cytology, and HPLC were used to study the differences in leaf morphology, structure, physiological characters, and alkaloid content in response to different irradiances. The results indicated that the highest foliar biomass was observed under I50 (50 of full sunlight) followed by I30 (30 of full sunlight) the highest net photosynthetic rate, stomatal conductance, transpiration rate values were observed under I30 followed by I50, and lower values occurred in I10 (10 of full sunlight) and I100 (full sunlight) With increased light intensity, total leaf area and the contents of chlorophyll a (Chl a) chlorophyll b (Chl b) and chlorophyll (Chl a+b) per unit leaf area were clearly reduced, whereas leaf mass per area, carotenoid content, leaf thickness, thickness of palisade and spongy parenchyma, and stomatal density were all significantly increased. Electron microscopic observation revealed that the number of grana, stroma lamellae and the number of starch grains in chloroplasts were decreased, the number of plastoglobuli was increased when irradiance levels increased. The estimated total yield of alkaloids in a single plant was higher under I30 and I50 than under I10 or I100 as a result of the higher biomass of the plants. Therefore, I30 and I50 were not only beneficial to increase biomass, but also suitable for the synthesis and accumulation of the major secondary metabolites (alkaloids) Our findings provide valuable data for the determination and regulation of irradiance levels during artificial cultivation of M. bodinieri.
Acta Physiologiae Plantarum