Abstract
Aquaporins (AQPs) are integral membrane proteins facilitating the transport of water and some small neutral molecules across cell membranes. In past years, much effort has been made to reveal the location of AQPs as well as their function in water transport, photosynthetic processes, and stress responses in higher plants. In the present review, we paid attention to the character of AQPs in determining carbon and nitrogen status. The role of AQPs during photosynthesis is characterized as its function in transporting water and CO2 across the membrane of chloroplast and thylakoid; recalculated results from published studies showed that over-expression of AQPs contributed to 25% and 50% increases in stomatal conductance (gs) and mesophyll conductance (gm), respectively. The nitrogen status in plants is regulated by AQPs through their effect on water flow as well as urea and NH4+ uptake, and the potential role of AQPs in alleviating ammonium toxicity is discussed. At the same time, root and/or shoot AQP expression is quite dependent on both N supply amounts and forms. Future research directions concerning the function of AQPs in regulating plant carbon and nitrogen status as well as C/N balance are also highlighted.
Highlights
As a member of the major intrinsic protein (MIP) families, Aquaporins (AQPs) have been demonstrated to be integral membrane proteins that function in facilitating water transport across biological membranes [1,2]
Nodulin-26-like intrinsic proteins (NIPs) are expressed in the peribacteroid membrane of N2-fixing symbiotic root nodules, but they are present in the plasma membrane or the endoplasmic reticulum of the nonlegume plant species [4]
It is proposed that the photosynthesis rate (Pn) in C3 plants is mainly limited by Rubisco carboxylation activity in full sunlight under the current atmospheric CO2 concentration, which emphasizes the critical role of both gs and gm in mediating carbon metabolism [33]
Summary
As a member of the major intrinsic protein (MIP) families, Aquaporins (AQPs) have been demonstrated to be integral membrane proteins that function in facilitating water transport across biological membranes [1,2]. Nodulin-26-like intrinsic proteins (NIPs) are expressed in the peribacteroid membrane of N2-fixing symbiotic root nodules, but they are present in the plasma membrane or the endoplasmic reticulum of the nonlegume plant species [4]. An uncharacterized AQP subfamily was recently identified in the genomes of lower plants and dicots and named X intrinsic proteins (XIPs) [6]. Some lower plant species have acquired additional aquaporins, including GlpF-like intrinsic protein (GIPs) and hybrid intrinsic proteins (HIPs). The function of AQPs was firstly reported as water channel proteins; later on, functional expression of plant AQPs in Xenopus oocytes and/or yeast cells pointed to. The regulation of AQP expression by nitrogen is discussed
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