Effect of elevated [CO₂] on cell structure and function in seed plants

Unprecedented increase in atmospheric carbon dioxide concentration [CO₂] is regarded as one of the key factors responsible for global climate change. Evidence from palaeo-records indicates a close relationship between variation in atmospheric [CO₂] and corresponding structural adaptations in plants. Exposure to elevated [CO₂] alters plant structure by inducing changes in rate of cell division, cell expansion and cell cycling. Alterations in plant structure under elevated [CO₂] at organ level is possibly a result of metabolic changes induced at cellular level. Chloroplast, the light-harvesting organelle, has been shown to be most seriously affected by high [CO₂]. Prolonged exposure to elevated [CO₂] induces accumulation of starch grains within chloroplasts leading to distortion of thylakoids. Higher rate of photosynthesis in plants grown at high [CO₂] is accompanied by increased number of mitochondria to meet high cellular energy demand. These ultrastructural observations are corroborated by studies on nuclear genome that have revealed up as well as down-regulation of several genes involved in photosynthetic and respiratory pathways. In some species, exposure to elevated [CO₂] results in accumulation of tannin-like vacuolar deposition, suggesting activation of phenylpropanoid pathway. Ultrastructural alterations in peroxisomes, endoplasmic reticulum, Golgi apparatus and cytoskeleton due to CO₂ enrichment have received less attention. It is imperative to understand cellular changes occurring with elevated [CO₂]so as to correlate these with the physiological alterations at plant level. A thorough insight into ultrastructural changes in response to increased carbon dioxide will provide a better, generalized understanding of plant response to rising atmospheric [CO₂] in future. Disruption of cell organelle structure and function may also indicate a wider impact of climate change across plant (and animal) groups.