Leaf Functional Anatomy in Relation to Photosynthesis

Abstract

Rubisco is a large enzyme with a molecular mass of approximately 550 kD. The maximum rate of CO 2 fixation (i.e. ribulose-1,5-bisphosphate [RuBP] carboxylation) at CO 2 saturation is only 15 to 30 mol CO 2 mol 21 Rubisco protein s 21 at 25°C. Affinity to CO 2 is also low, and the K m , K c , at 25°C in the absence of oxygen is comparable to the CO 2 concentration in water equilibrated with air containing 39 Pa CO 2 (approximately 390 mL L 21 ), 13 mM. Moreover, RuBP carboxylation is competitively inhibited by RuBP oxygenation, which is the primary step of the energy-wasting process, photorespiration. If the CO 2 concentration in the chloroplast stroma is low, the carboxylation rate will decrease while the oxygenation rate will increase. Under such conditions, light energy and other resources, including nitrogen and water, are all wasted, eventually leading to a decrement of fitness of the plants. From these data, we may consider that structural features of the leaf contributing to the maintenance of the high CO 2 concentration in the chloroplast stroma may have been selected during evolution.In this Update, we focus on the key structural features that affect CO 2 concentration in the chloroplast stroma. First, we analyze the conductance for CO 2 diffusion from the substomatal cavity to the chloroplast stroma (mesophyll conductance [g m ], also called internal conductance). Because the low g m limits photosynthesis,

The Cytoplasmic Carbonic Anhydrases βCA2 and βCA4 Are Required for Optimal Plant Growth at Low CO2

“…From these measurements, it was concluded that the cytoplasmic CAs do not play an important role in photosynthesis. These observations are in agreement with the models of Badger and Price (1994), Terashima et al, (2011), and Tholen et al (2012Tholen et al ( , 2014. They argued that the cytoplasm offers only minimal resistance to CO 2 diffusion because the chloroplasts are often close to the plasma membrane in mesophyll cells.…”

“…CAs in the cytosol and chloroplast have been proposed to help facilitate the diffusion of inorganic carbon to the chloroplast; however, recent modeling studies indicate that the effect of CA activity in the cytoplasm might be minimal (Badger and Price, 1994;Terashima et al, 2011;Tholen et al, 2012Tholen et al, , 2014. Earlier studies using antisense lines show that reducing chloroplast CA levels below 10% of total CA activity in tobacco did not significantly reduce photosynthesis rates Price et al, 1994;Williams et al, 1996).…”

Nutrient Use Strategy of Carpinus cordata Saplings Growing under Different Forest Stand Conditions

“…포함한 많은 세포 기관의 구성성분이고, 광합성을 비 롯한 다양한 생리적 반응과 그 중간단계에서 중심적인 역할을 한다 (Hirose and Werger, 1987;Terashima et al, 2011;Pang et al, 2014). (Vitousek et al, 2010), 흡수된 양분의 분배는 수관 내 양분 요구 도, 광의 분포 등에 영향을 받게 된다 (Dewar et al, 2012;Kobe et al, 2005;Niinemets, 2012).…”

Photosynthetic Productivity: Can Plants do Better?

“…After passage through the stomata, CO 2 diffusion from the intercellular space into the stroma where carboxylation occurs depends upon a series of conductances that are referred to collectively as the internal or mesophyll conductance (Terashima et al, 2011). As it turns out, these combined internal conductances substantially limit photosynthesis, and explain nearly half of the drawdown in CO 2 concentration between the atmosphere and the stroma (Ca -Cc; Warren, 2008).…”

“…Physical barriers (e.g. cell wall and membranes) and gas-to liquid-phase transitions between the external air and the enzymatic site of carbon fixation lowers the diffusional conductance between the atmosphere and the stroma (Terashima et al, 2011). Conductance limited diffusion from Ca to Ci to Cc varies among species and with environmental conditions and can strongly limit photosynthesis (Warren, 2008).…”