Proteins functionally and immunogenically related to pathogenesis‐related proteins are induced during parsley leaf senescence

The advancement of leaf senescence is accompanied by a reduction in cellular protein content together with the induction of specific proteins which are probably involved in the process. In the present study, with parsley, we followed the changes in the levels of proteins functionally and immunogenically related to pathogenesis‐related proteins during both senescence of detached leaves and natural senescence of attached leaves. Both chitinase activity and protein level were found to be induced during senescence, as was the level of two other proteins immunologically related to β‐1,3‐glucanase and P4 pathogenesis‐related proteins of citrus and tomato, respectively. A high correlation between the advancement of senescence and the induction of these proteins was demonstrated. Treatments with CO₂ or gibberellic acid, which retard senescence, reduced both chitinase activity and the level of the pathogenesis‐related proteins, whereas enhancement of senescence with ethylene induced them further. The induction of pathogenesis‐related proteins during senescence suggests that these proteins may have a primary role in this process.     

Increase of Fusarium Rot in Stored Citrus Fruit

In recent years the incidence of Fusarium spp. isolated from Stem End Rot (SER) and Internal Core Rot (ICR) of grapefruit and oranges has increased markedly. Fusarium spp. were isolated from apparently healthy green buttons and from the tissue underneath the button of healthy fruits. Of all the SER- and ICR-rotted fruit, the incidence of Fusarium spp. alone and of Fusarium spp. with Alternaria citri was between 75 and 100%. Fusarium was also found to be the single causal agent of ICR of oranges and grapefruit. Species of Fusarium isolated from Stem End Rot and Internal Core Rot of citrus fruit were F. oxysporum, F. moniliforme and recently also F. culmorum.     

The characterization of LeNUC1, a nuclease associated with leaf senescence of tomato

Induction of nuclease and RNase activities, together with decreases in nucleic acid content are considered to be characteristics of senescence in higher plants. However, little is known about the specific identities or functions of the enzymes involved or the mechanisms controlling their activation. Here we report the identification of a 41-kDa-tomato nuclease, LeNUC1, which is specifically induced during tomato leaf senescence but not in ripening fruits. LeNUC1 is a glycoprotein, which can degrade both RNA and DNA and has optimal activity at pH 7.5–8. EDTA inhibits the activity of LeNUC1, while the addition of Co²⁺ or Mn²⁺ can restore its activity in the presence of the chelating agent. Interestingly, the activity of LeNUC1 is also induced in young leaves upon treatment with ethylene, which is known to be a senescence-promoting hormone in tomato. Constitutive activity of a 39-kDa nuclease, LeNUC2, similar in its biochemical requirements to LeNUC1, was also detected. LeNUC2 is not induced by ethylene and does not seem to be glycosylated. Based on their characteristics, LeNUC1 and LeNUC2 can be classified as Nuclease I enzymes. LeNUC1 may be involved in nucleic acid metabolism during tomato leaf senescence.