Chlorosis

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In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and may die unless the cause of its chlorophyll insufficiency is treated; some chlorotic plants, such as the albino Arabidopsis thaliana mutant ppi2 are viable if supplied with exogenous sucrose^[1]. Specific nutrient deficiencies (often aggravated by high soil pH) produce chlorosis, which may be corrected by supplemental feedings of iron, magnesium or nitrogen compounds in various combinations. Some pesticides, particularly herbicides, may also cause chlorosis, both to target weeds and occasionally to the crop being treated.

The reason iron deficiency causes chlorosis is that iron is used in the active site of glutamyl-tRNA reductase, an enzyme needed for the formation of 5-Aminolevulinic acid which is a precursor of heme and chlorophyll.^[2]

[edit] Chlorosis in viticulture

Grape vines are suscpetible to chlorosis just like many other plants, and the symptoms of iron deficiency tend to be common on soils rich in limestone. In the wake of The Great French Wine Blight, when European Vitis vinifera were affected by Phylloxera, chlorosis became a more problematic phenomenon in viticulture. To solve the Phylloxera problem, V. vinfiera was grafted onto rootstock based on American species of the Vitis genus, such as Vitis riparia, Vitis rupestris, Vitis berlandieri. However, many of these were less adapted to the lime-rich soils that was common in many of France's vineyards, in particular many of those that produced wines of top quality. Many grafted vines in lime-rich vineyards therefore showed signs of iron deficiency, and this specific form of chlorosis was termed chlorose calcaire in France. The problem was largely overcome by the selection of lime-resistant American vines as basis for hybrid vines used for rootstock material. However, since such rootstocks may be less than optimal in other respects, it is necessary for the viticulturalist to balance the need for chlorosis resistance against other viticultural needs. This is illustrated by one of the most common lime-resistant rootstocks, 41 B, which is a hybrid between V. vinifera cultivar Chasselas and V. berlandieri, which generally has a sufficient, but not extremely high, Phylloxera resistance.^[3][4]

[edit] Etymology

Chlorosis is derived from the word Chloris or from the Greek Khloros meaning "greenish-yellow," "pale green," "pale," "pallid" or "fresh".

[edit] References

1. ^ Functional Specialization amongst the Arabidopsis Toc159 Family of Chloroplast Protein Import Receptors
2. ^ A. Madan Kumar and Dieter Söll, Antisense HEMA1 RNA Expression Inhibits Heme and Chlorophyll Biosynthesis in Arabidopsis, Plant Physiol, January 2000, Vol. 122, pp. 49-56 http://www.plantphysiol.org/cgi/content/full/122/1/49
3. ^ "Chlorosis". Oxford Companion to Wine (Third Edition). (2006). Ed. Jancis Robinson. Oxford: Oxford University Press. 170. ISBN 0-19-860990-6. 
4. ^ "Rootstock". Oxford Companion to Wine (Third Edition). (2006). Ed. Jancis Robinson. Oxford: Oxford University Press. 591-593. ISBN 0-19-860990-6. 

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