Exposure to low levels of photosynthetically active radiation induces rapid increases in palisade cell chloroplast volume and thylakoid surface area in sunflower (Helianthus annuus L.)

Abstract

Summary. Sudden changes in photoactive radiation (PAR) (wavelength, 400-700 nm) induces rapid surface area changes in chloroplast thylakoid membranes. Although this response may have important photo-acclimative functions for the plant, little is known about the mechanisms by which changes in irradiance are detected or how thylakoid membranes actually increase or decrease surface area. Knowledge of the time required for significant changes in thylakoid area would help eliminate or support several possible mechanisms that may be involved in this aspect of photo-acclimation in plants. Leaf tissues were acclimated to a PAR of 500 ~tmol quanta per m 2 per s then exposed to low irradiance (PAR, 50 gmol quanta per m 2 per s) and sampled at 5, 15, 30, and 60 min post exposure. Tissue and cell structure were quantified and results showed a significant increase in the surface-to-volume ratio and surface area per unit of standard leaf volume for both appressed and nonappressed thylakoids within 5 min of exposure to low irradiance. On the basis of the ratios of appressed to nonappressed thylakoids, the surface area of the nonappressed thylakoids was found to increase faster than that of the appressed thylakoids throughout the sample period. The portion of the appressed thylakoids in contact with the stroma was defined as margin thylakoids. Margin thylakoid surface-tovolume ratio did not change relative to the high-irradiance control during the sample period but did remain significantly lower than the low-irradiance control during the sample period. The ratio of appressed to margin thylakoids indicated a broadening and shortening of the appressed thylakoid stack within the first 5 min of lowirradiance exposure. The rapidity of the shade response indicates that the early events in this response probably do not directly involve gene activation pathways.

Anatomy, chlorophyll content and photosynthetic potential in grapevine leaves under plastic cover

“…The last one influences more the plants in their metabolic process related to gas exchange (ChAVARRiA et al, 2008a). The photosynthetic apparatus of plants under shaded conditions should be dynamic so that it can respond accordingly to restricted solar radiation (WhELLER;FEGERBERG, 2000). Solar radiation is the determining factor of the photosynthetic process (SiLVESTRini et al, 2007).…”

Role of Crop Load in Chloroplast Ultra-structure and Zonal Chlorosis, a Physiological Disorder in ‘Honeycrisp’ Apple Trees

“…This suggests a role for water deficit in zonal chlorosis, although water deficit also is often associated with increased sunlight and is difficult to separate in field studies. Wheeler and Fagerberg (2000) have demonstrated a role in ultraviolet A and ultraviolet B levels in increasing chloroplast volume and starch granule accumulation in sunflower leaves.…”

Unbiased Estimation of Norway Spruce (Picea Abies L. Karst.) Chloroplast Structure: Heterogeneity Within Needle Mesophyll Under Different Irradiance and [Co2]

“…For chloroplast ultrastructural studies in broad leaves, the first or upper layers of leaf photosynthetic tissue, mesophyll, ( Fig. 1A) are often analysed (Günthardt-Goerg et al, 2000;Wheeler and Fagerberg 2000;Valkama et al, 2003;Velikova et al, 2009;Sun et al, 2011;Mašková et al, 2017). The first layer of mesophyll receives more incident irradiance than its deeper layers and thus, it can be regarded as the most important layer for photosynthesis.…”