The effect of light intensity and temperature on plant growth and chloroplast ultrastructure in soybean

TLDR: Differences in growth rate, leaf anatomy, chloroplast ultrastructure, and chemical composition in soybean plants grown in cabinets under combinations of temperature and light similar to those occurring naturally are concerned.

Abstract: A B S T R A C T Soybean plants grown in controlled environment cabinets under light intensities of 220 w/m2 or 90 w/m2 (400-700 nm) and day to night temperatures of 27.5-22.5 C or 20.0-12.5 C in all combinations, exhibited differences in growth rate, leaf anatomy, chloroplast ultrastructure, and leaf starch, chlorophyll, and chloroplast lipid contents. Leaves grown under the lower light intensity at both temperatures had palisade mesophyll chloroplasts containing well-formed grana. The corresponding leaves developed under the higher light intensity had very rudimentary grana. Chloroplasts from high temperature and high light had grana consisting of two or three appressed thylakoids, while grana from the low temperature were confined to occasional thylakoid overlap. Spongy mesophyll chloroplasts were less sensitive to growth conditions. Transfer experiments showed that the ultrastructure of chloroplasts from mature leaves could be modified by changing the conditions, though the effect was less marked than when the leaf was growing. LITTLE IS known concerning the influence of light intensities and temperatures characteristic of field conditions on the chloroplast ultrastructure of developing and mature leaves of normal plants. Bjorkman and Holmgren (1963) using the light microscope showed that their higher light intensity destroyed the chloroplasts of shade ecotypes of Solidago virgaurea, whereas chloroplasts from exposed ecotypes were unaffected. The effect of light intensity on the ultrastructure of chloroplasts from pigment-deficient mutants was investigated by Walles (1965), Schmid, Price, and Gaffron (1966), Clewell and Schmid (1969); the effect of temperature and light on the greening of detached, etiolated leaves by Klein (1960), Eilam and Klein (1962); and the eff ect of transference of dark-grown seedlings to light by \'IcWilliam and Naylor (1967). This study concerned differences in growth rate, leaf anatomy, chloroplast ultrastructure, and chemical composition in soybean plants grown in cabinets under combinations of temperature and light similar to those occurring naturally. Comparisons were made with plants grown outside and in the glasshouse. The plants used were well beyond the seedling stage.