Abstract
Background
Photosynthesis of plant non-leaf blade green tissue has been studied in some plants, but the photosynthesis characteristics of stem and petiole are poorly understood. Cucurbitaceous plants are climbing plants, and have a large biomass of stem and petiole. Understanding the photosynthetic contribution of cucumber stem and petiole to growth and the underlying molecular mechanisms are important for the regulation of growth in cucumber production.
Results
Here, the photosynthetic capacity of cucumber stem and petiole were proved by 14CO2 uptake. The total carbon fixation of stem and petioles is around 4% to that of one leaf blade in cucumber seedling stage, while the proportion of carbon accumulated in stem and petioles redistributed to sink organs (root and growing point) is increased obviously under leaf less condition. Photosynthetic properties of cucumber stem and petiole were studied using a combination of electron microscopy, chlorophyll fluorescence imaging and isotope tracer to compare with leaf blade using two genotype of cucumber (dark green and light green stems). Compare with leaf blade, chlorophyll contents of cucumber stem and petiole are lower, and accompanying with lower chloroplast number, lower stoma number, but with higher thylakoid grana lamella number and larger stomata size. The total photosynthetic rate of stem and petiole is equivalent to 6 ~ 8% of one leaf blade, but the respiration rates were simiar in all the three tissues, which shown an almost 0 net photosynthetic rate in stems and petioles, and with lower non-photochemical quenching (NPQ). Transcriptome analysis showed that compared with leaf blade, there are significantly different gene expressions in photosynthesis, porphyrin and chlorophyll metabolism, photosynthetic antenna proteins and carbon fixation in stem and petiole. Although with lower Rubisco expression level in stem and petiole, Rubisco and PEPC enzyme activities were both higher in stem and petiole than in leaf blade, suggesting the photosynthetic and respiratory mechanisms in stem and petiole are different from those in leaf blade.
Conclusions
In this study, we confirmed the photosynthetic contribution to growth of cucumber stem and petiole, and shown their similar photosynthetic pattern in tissue anatomy, molecular biology and physiology.
IMPACT OF ULTRAVIOLET-B RADIATION ON PHOTOSYSTEM II ACTIVITY AND ITS RELATIONSHIP TO THE INHIBITION OF CARBON FIXATION RATES FOR ANTARCTIC ICE ALGAE COMMUNITIES1
