MESA AND MEJA INCREASE STEADY-STATE TRANSCRIPT LEVELS OF ALTERNATIVE OXIDASE AND RESISTANCE AGAINST CHILLING INJURY IN SWEET PEPPERS (CAPSICUM ANNUUM L.)

Authors: FUNG, RAYMOND - HORT RES, NZ; Wang, Chien; Smith, David; Gross, Kenneth; TIAN, MEISHENG - HORT RES, NZ

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2003
Publication Date: 5/1/2004
Citation: Fung, R.W., Wang, C.Y., Smith, D.L., Gross, K.C., Tian, M. 2003. Mesa and meja increase steady-state transcript levels of alternative oxidase and resistance against chilling injury in sweet peppers (capsicum annuum l.). Plant Science. 166(2004) 711-719

Interpretive Summary: Sweet peppers are susceptible to chilling injury when stored at cold temperatures below 7 ºC for about 1 week. Damage caused by low temperature severely reduces their quality and storage life. We found that certain natural plant compounds (methyl salicylate and methyl jasmonate) increased resistance to chilling injury in green bell peppers. Because of the potential usefulness of these compounds in extending postharvest longevity of produce, it is important to understand the mechanism involved. Therefore, we determined the effect of these compounds on the expression of genes that are involved. During the period before the appearance of chilling injury symptoms, we found a gene that behaved very interestingly. Overnight pretreatment with these natural compounds increased the expression of the gene, and this increase was correlated with reduced chilling injury. The work presented here points to the possibility of using natural plant compounds to increase resistance to chilling injury in peppers and a broad range of other tropical crops. This information will be useful to other scientists as well as the produce industry, and will ultimately benefit consumers.

Technical Abstract: Methyl salicylate (MeSA) and methyl jasmonate (MeJA) vapors increased resistance against chilling injury in green bell pepper (C. annuum L. cv Century). The period within 2 days of cold storage was considered the most critical because chilling injury symptom (surface pitting) was not apparent. The expression patterns of alternative oxidase (AOX) and seven other genes involved in defense against oxidative stress before and during the early chilling period suggested that pre-treatment of pepper fruit with MeSA or MeJA vapors increased preferentially the transcript levels of AOX. Transcript levels of AOX (1.5 kb) were increased by storage at low temperature but the steady-state mRNA accumulation rate was faster at 0 ºC than at 5 ºC. Overnight treatment with MeSA or MeJA vapors increased transcript levels of AOX (1.5 kb) even at room temperature of 25 ºC, whereas no change was observed with untreated control. In addition to the expected 1.5 kb AOX transcript, RNA gel blot analysis revealed an extra 3.5 kb transcript that was induced only at 0 ºC. At 0 ºC, both AOX transcripts (1.5 and 3.5 kb) reached maximal levels firstly in MeSA treated fruit, secondly in MeJA treated fruit and lastly in controls. AOX transcript levels were maintained at a high level as long as the fruit were kept at 0 ºC. Alternative respiratory pathway was proposed to mediate chilling injury. Here, we show that the increase in AOX transcript levels by MeJA or MeSA before cold treatment was correlated with reduced incidence of chilling injury.