Nucleotide sequence of a cDNA clone encoding 1-aminocyclopropane-1-carboxylate synthase in mustard (Brassica juncea [L.] Czern & Coss)

Cyanide produced with ethylene by ACS and its incomplete detoxification by β-CAS in mango inflorescence leads to malformation

Malformation of mango inflorescences (MMI) disease causes severe economic losses worldwide. Present research investigates the underlying causes of MMI. Results revealed significantly higher levels of cyanide, a by-product of ethylene biosynthesis, in malformed inflorescences (MI) of mango cultivars. There was a significant rise in ACS transcripts, ACS enzyme activity and cyanide and ethylene levels in MI as compared to healthy inflorescences (HI). Significant differences in levels of methionine, phosphate, S-adenosyl-L-methionine, S-adenosyl-L-homocysteine, ascorbate and glutathione, and activities of dehydroascorbate reductase and glutathione reductase were seen in MI over HI. Further, a lower expression of β-cyanoalanine synthase (β-CAS) transcript was associated with decreased cellular β-CAS activity in MI, indicating accumulation of unmetabolized cyanide. TEM studies showed increased gum-resinosis and necrotic cell organelles, which might be attributed to unmetabolized cyanide. In field trials, increased malformed-necrotic-inflorescence (MNI) by spraying ethrel and decreased MNI by treating with ethylene inhibitors (silver and cobalt ions) further confirmed the involvement of cyanide in MMI. Implying a role for cyanide in MMI at the physiological and molecular level, this study will contribute to better understanding of the etiology of mango inflorescence malformation, and also help manipulate mango varieties genetically for resistance to malformation.

Identification and characterization of cDNAs encoding ethylene biosynthetic enzymes from Pelargonium x hortorum cv Snow Mass leaves

Two Pelargonium 1-aminocyclopropane-1-carboxylate (ACC) synthase cDNAs (GAC-1 and GAC-2) were identified and characterized. GAC-1 is 1934 bp long with a 1446-bp open reading frame encoding a 54.1-kD polypeptide. GAC-2 is a 1170-bp-long ACC synthase polymerase chain reaction fragment encoding 390 amino acids. Expression of GAC-1 and GAC-2 together with a previously identified ACC oxidase (GEFE-1) was examined in different Pelargonium plant parts, and leaves were subjected to osmotic stress (sorbitol), metal ion stress (CuCl2), auxin (2,4-dichlorophenoxyacetic acid [2,4-D]), and ethylene. GAC-1 expression was not detectable in any of the plant parts tested, whereas high levels of GAC-2 were expressed in the leaf bud, young leaf, young floret, fully open floret, and senescing floret. GAC-2 was expressed to a lesser degree in fully expanded leaves or roots and was undetectable in old leaves and floret buds. GEFE-1 was detectable at all leaf ages tested, in young and fully open florets, and in the roots; however, the highest degree of expression was in the senescing florets. GAC-1 was induced by sorbitol. Both GAC-1 and GAC-2 were only slightly affected by CuCl2 and induced indirectly by 2,4-D. GEFE-1 was highly induced by sorbitol, CuCl2, and 2,4-D. GAC-1, GAC-2, and GEFE-1 were unaffected by ethylene treatment. These results suggest that GAC-1 is only induced by stress and that GAC-2 may be developmentally regulated, whereas GEFE-1 is influenced by both stress and development.