Still, the actual Cycloheximide number of chloroplasts in a mature leaf cell as well as the abundance of pigments within each chloroplast depends on both the developmental stage of particular tissues and environmental stimuli. Plants must use overlapping networks to coordinate chloroplast development with a plethora of environmental inputs in order to maintain balance between rates of photosynthesis and metabolism. Light amount and quality are powerful regulators of chlorophyll biosynthesis and chloroplast development. Light also establishes circadian and diurnal cycles that provide a constant internal control over gene expression and when in tune with environmental signals, plants display maximum growth. Nitrogen is required for building biological molecules and is therefore also intrinsically linked to both photosynthetic activity and the overall carbon status of the plant. Nitrogen assimilation in the chloroplast is a prerequisite for chlorophyll biosynthesis, specifically by building up the glutamate pool. The Glutamine Synthetase/Glutamate Synthase pathway is a key point in nitrogen assimilation where ammonium is incorporated into glutamate, providing the precursor for production of all amino acids, nucleic acids and chlorophylls. The subsequent steps involved in chlorophyll biosynthesis are well documented and involve a number of key rate-limiting enzymes. HEMA1 encodes a Glu-tRNA reductase enzyme that controls flux through the tetrapyrrole biosynthetic pathway and leads to production of 5-aminolevulinic acid from which the porphyrin ring system is derived. GENOMES UNCOUPLED 4 subsequently binds protoporphyrin chlorophyll intermediates, stimulates Mg chelatase activity, and has also been implicated in plastidic retrograde signaling to regulate nuclear gene expression. Light-dependent reduction of protochlorophyllide to chlorophyllide is catalyzed by NADPH:protochlorophyllide oxidoreductase in mature leaves, where the genes PORB and PORC form a redundant system regulating chlorophyll biosynthesis. Whilethese genes demonstrate circadian and diurnal patterns of expression, the exact mechanism by which chlorophyll GDC-0941 content is adjusted with varying amounts of light and nitrogen is not well documented. Because nitrogen is a key component of the chlorophyll molecule, the concentration of nitrate available to a plant directly influences chlorophyll biosynthesis and chloroplast development. Chlorophyll content is a key indicator of plant health and can be used to optimize nitrogen fertilizer application in order to potentiate larger crop yields with lower environmental load. A subset of nitrate responses are mediated by the class of plant hormones know as cytokinins, whose synthesis and transport is linked to the nitrogen status of the plant.