Plants grow in a dynamic environment. Their growing and development are influenced by abiotic ( environmental ) and biotic emphasiss. These emphasiss are the primary cause of harvest loss worldwide. They can cut down the mean outputs of harvest workss by more than 50 % ( Bartels & A ; Sunkar, 2005 ) .
There are so many environmental emphasiss finding works growing, distribution, and development. One of the most of import environmental emphasiss is limited H2O. This emphasis leads to cellular desiccation. It causes osmotic emphasis and H2O remotion from cytol into excess cellular infinite, so the cytosolic and vacuolar volume are reduced ( Bartels & A ; Sunkar, 2005 ) .
Water restriction induces a scope of physiological and biochemical responses in workss such as stomatous closing, repression of cell growing and photosynthesis, and activation of respiration ( Lu et al. , 2007 ) . Plants besides respond and adapt to H2O shortage at cellular and molecular degree, . For illustration, they accumulate specific osmolytes and proteins that are involved in stress tolerance.
Furthermore, Plants have developed assorted survival mechanisms to get the better of continued exposure to limited H2O. For illustration a stress-signal transduction which leads to assorted physiological and metabolic responses such as emphasis antiphonal cistron look ( Lu et al. , 2007 ) . This mechanism will assist workss last if they subject to limited H2O.
Numerous cistrons with diverse maps are induced or repressed by abiotic emphasis ( Yamaguchi-Shinozaki & A ; Shinozaki, 2005 ) . Although 100s of cistrons have been found to be involved in abiotic emphasis responses. A figure of these cistrons have been good characterized, but the maps of most of the cistrons are still unknown. And there are high possibilities to detect more cistrons involved in abiotic emphasiss that presently have n’t discovered yet. Most of their cistron merchandises may work in stress response and tolerance at the cellular degree.
Now, analysing the maps of these cistrons is of import. It will assist us to make farther apprehension of the molecular mechanisms of works emphasis response and tolerance. And finally it will take to enhancement of stress tolerance in harvest workss through familial use ( Shinozaki & A ; Yamaguchi-Shinozaki, 2007 ) .
Research conducted by Kimmerer and Kozlowski ( 1982 ) shown that under emphasis status, works produce high degree of ethene, C2H6, ethanal, and ethanol. This consequence indicated that ethene can be an index of emphasis. Micro array analysis on Arabidopsis conducted by Seki et Al. ( 2001 ) shown that during limited H2O, cistrons encode ACC oxidase enzyme were up-regulated. Contrary, cistrons encode ACC synthase enzyme were down-regulated. This phenomenon indicated the possibility of a different ordinance system in ethylene biogenesis on works during limited H2O.
Ethylene is one of works endocrines. It is involved in works growing and development such as seed sprouting, blossoming, fruit maturation, aging, and abscission of assorted variety meats ( Abeles et al. , 1992 ) . Ethylene is synthesized from methionine ( Figure 1. ) . First, methionine is converted to S-adenosylmethionine ( SAM or Adomet ) . SAM will be converted to 1-aminocyclopropane-1-carboxylic acid ( ACC ) by ACC synthase enzyme. Finally ACC will be converted to ethylene by ACC oxidase enzyme ( Yang and Hoffman, 1984 ) .
Figure 1. The ethylene biosynthetic tract. ( AdoMet: S-adenosyl-methionine ; Met: methionine ; ACC: 1-aminocyclopropane-1-carboxylic acid ; MTA: methylthioadenine. Adopted from: Argueso et al. , 2007 )
The rate-limiting measure in ethylene production is the transition of SAM to ACC, but the recent molecular surveies have shown that the specific look of ACC oxidase cistrons dramas of import function in the ordinance of ethylene biogenesis. ACC oxidase enzyme plays a regulative map in ethylene production in fruits like tomato, apple, and banana ( Choudhury et al. , 2008 ) .
ACC SYNTHASE and ACC OXIDASE Genes
Gene that encode ACC synthase ( ACS ) and ACC oxidase ( ACO ) in many works species have been cloned and identified. Both enzymes are encoded by multigene households. The figure of ACS and ACO cistron household member varies between species. It has been reported that there are eight ACS cistrons in tomato ( Llop-Tous et al. , 2000 ) , i¬?ve in murphy ( Schlagnhaufer et al. , 1997 ) , and six in rice ( Rzewuski & A ; Sauter, 2008 ) . In Arabidopsis at least there are 12 cistrons that encode ACS enzyme. From those, eight cistrons encode active enzyme, one cistron ( AT-ACS1 ) encode inactive enzyme, one pseudo-gene ( AT-ACS3 ) and two cistrons encode enzyme which have transaminase activity.
For ACC oxidase, there are four in tomato ( Llop-Tous et al. , 2000 ) , four in apple ( Binnie & A ; McManus, 2009 ) , and six in rice ( Rzewuski & A ; Sauter, 2008 ) . Five ACO cistrons were found through computational analysis in the Arabidopsis thaliana genome. They are AT-ACO1, AT-ACO2 and AT-ACO4 and 2 putative ACO.
The look of ACC syntase and ACC oxidase cistrons in higher workss is regulated developmentally and environmentally. These cistrons are expressed differentially in response to different signals such as the signals associated with maturation, injuring, aging, biotic and abiotic emphasiss. A broad scope of abiotic emphasiss including drouth, high or low temperature, implosion therapy, metal, and salt can bring on the synthesis of ethene.
AT-ACS2 is induced by cycloheximide, injuring and ethylene exposure for two hours. However, drawn-out ethene intervention decreases its look. Expression of AT-ACS4 in seedling is induced by cycloheximide, indoleacetic acid and wounding. AT-ACS5 is antiphonal to cytikinin and AT-ACS6 is induced by ozone, nitrile, indol acetic acid and ethene ( KA™pczyA„ski & A ; KA™pczyA„ska, 2005 ) .
Analysis of AT-ACS booster showed that AtACS7 responds to a high salt intervention emphasis. Furthermore, drought emphasis consequences in a little lessening in the look of AtACS5 and AtACS7 cistrons ( Wang et al. , 2005 ) .
Genes encode ACC oxidase are up-regulated in response to limited H2O. At the same clip, cistrons encode ACC synthase are down-regulate ( Seki et al. , 2001 ) .
Although the function of ethene in developmentally regulated aging has been extensively studied, its function in the ordinance of drought-induced foliage aging is less good understood. In corn, Mu-insertion mutations in the ACS cistrons ZmACS2 and ZmACS6 produce less ethylene than wild-type workss and besides show delayed drought-induced aging ( Argueso et al. , 2007 ) .
ACS and ACO Gene Silencing
Ethylene production can be reduced by take downing the look of ACC synthase cistrons utilizing antisense engineering. An antisense orientation of ACC synthase cistron was transformed into tomato workss. The ethylene production in the transgenic workss decreased by about 99 % compared to normal works ( KA™pczyA„ski & A ; KA™pczyA„ska, 2005 ) .
Similar to the instance of ACC synthase, antisense engineering has been used to suppress synthesis of ACC oxidase. Gao et Al. ( 2007 ) have knocked down ACC oxidase cistrons in pear by utilizing antisense complementary DNA encoding ACC oxidase. Ethylene production was reduced by 85 % in an antisense line.
Xiong et Al. ( 2004 ) have successfully knocked down the look of ACO cistron in tomato utilizing dual strand RNA ( dsRNA ) . When the concept with the 7-nt linker was used, 69 % of the transformed workss had full-RNA intervention. Conversely, merely 9.6 % of the transformed workss had full-RNA intervention when 1,002-bp linker was used.
Research conducted by Smith et Al. ( 2000 ) and Baena-Gonzales et Al. ( 2007 ) showed that cistron concept encoding intron-spliced RNA with a hairpin construction can bring on post-translation cistron silencing ( PTGS ) with about 100 % efficiency when directed against endogenous cistrons.