Masayasu Nagata

Ripening-associated ethylene biosynthesis in tomato fruit is autocatalytically and developmentally regulated

To investigate the regulatory mechanism(s) of ethylene biosynthesis in fruit, transgenic tomatoes with all known LeEIL genes suppressed were produced by RNA interference engineering. The transgenic tomato exhibited ethylene insensitivity phenotypes such as non-ripening and the lack of the triple response and petiole epinasty of seedlings even in the presence of exogenous ethylene. Transgenic fruit exhibited a low but consistent increase in ethylene production beyond 40 days after anthesis (DAA), with limited LeACS2 and LeACS4 expression. 1-Methylcyclopropene (1-MCP), a potent inhibitor of ethylene perception, failed to inhibit the limited increase in ethylene production and expression of the two 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) genes in the transgenic fruit. These results suggest that ripening-associated ethylene (system 2) in wild-type tomato fruit consists of two parts: a small part regulated by a developmental factor through the ethylene-independent expression of LeACS2 and LeACS4 and a large part regulated by an autocatalytic system due to the ethylene-dependent expression of the same genes. The results further suggest that basal ethylene (system 1) is less likely to be involved in the transition to system 2. Even if the effect of system 1 ethylene is eliminated, fruit can show a small increase in ethylene production due to unknown developmental factors. This increase would be enough for the stimulation of autocatalytic ethylene production, leading to fruit ripening.

Prediction and suppression of internal blue discoloration in roots of daikon, the Japanese radish (Raphanus sativus L.)

Abstract The internal blue discoloration of edible daikon roots often occurs on day 3 after harvest during storage at 20°C and is a serious problem. This study reports a rapid and simple method for predicting discoloration at harvest and proposes two methods for suppressing the discoloration of roots that are at discoloration risk. The soaking of freshly harvested roots in aqueous hydrogen peroxide resulted in immediate blue discoloration. The correlation between discoloration after storage at 20°C and discoloration after soaking in hydrogen peroxide was positive. Discoloration using hydrogen peroxide at harvest is a useful way of predicting discoloration risk. The storage of roots at 10°C in air or at 20°C in an atmosphere containing 1% (v/v) molecular oxygen resulted in no discoloration for at least 8 days. These storage conditions can guarantee no discoloration for the distribution after harvest.

Effects of Temperature and Light Intensity on Ascorbic Acid Content in Cotyledons of Japanese Radish

The relationship between L-ascorbic acid (AsA) content in cotyledons of Japanese radish and temperature or light intensity during growth was investigated. Japanese radish seedlings were grown in the dark at 15, 20, 25, 30, or 35°C. The maximum rate of hypocotyl elongation occurred at 25°C treatment compared with other temperature treatments. However, lower temperatures led to higher maximum content of AsA in cotyledons on a fresh weight basis. At temperatures below 30°C, AsA content in cotyledons increased rapidly, reaching a maximum 3-5 days after sowing and subsequently declined. Japanese radish seedlings were grown under various light intensity conditions at 25°C. Illumination led to increase of AsA content in cotyledons. A linear relationship was observed between the AsA content and the logarithms of light intensity.

Evaluation of Some Commercial Ethylene Absorbents and Natural Materials for their Efficiency

Some commercial ethylene absorbents and natural materials were evaluated for their ethylene removal efficiency at different moisture conditions. Among the 13 commercial ethylene absorbents, 6 of them had some deficiencies in the ethylene removal rate or efficiency even under dry conditions. Three of the ethylene absorbents such as artificial zeolite lost their efficiency at high humid conditions. Five of the absorbents released the absorbed ethylene when they were moistened with water. Four of the commercial ethylene absorbents, for example, activated carbon with palladium chloride and molecular sieve treated with potassium bromate, were effective at all moisture conditions. No significant ethylene removal effect was found in natural materials such as green tuff (Oyaishi) and rice hulls. Packed broccoli with polyethylene film was stored at 10°C with or without ethylene absorbents, and the chrolophyll, ascorbic acid and surface color were analyzed. The activated carbon with palladium chloride showed the better effect on the retention of freshness than the activated carbon or artificial zeolite. The results obtained by the evaluation of ethylene absorbents and the effect of ethylene absorbents on the retention of freshness of broccoli were well correlated.

Studies on Sensitivity of Vegetables to Low Oxygen (Part III). Effect of Low Oxygen Atmosphere on Respiration of Several Vegetables (II).

青果物の呼吸に及ぼす低酸素の影響を調べるためにPSA (pressure swing adsorption) 方式修整空気システム (PSA-MAS) ・CO2発生量測定装置を開発した。本装置および先に開発したガス分離膜方式修整空気システム (GSM-MAS) ・CO2発生量測定装置を用いてカリフラワー, セルリー, コマツナ, レタス, ブロッコリー, キャベツの呼吸量を測定した。呼吸量は野菜が排出する二酸化炭素の割合を, 空気下および酸素濃度1%, 4%, 7%, 10%, 温度10℃環境下で測定した。空気下に比べ, 実験に供した全ての野菜において低酸素環境下で呼吸量が低下したが, 品目により低酸素環境下におかれた後の呼吸応答に違いが見られ, それらの違いは3つのグループに分けることができた。(1) 低酸素条件に対し呼吸量の低下が極めて速く, 呼吸量が抑制された後その呼吸量の抑制程度が実験終了時まで維持されたもの (カリフラワー, セルリー)。(2) 低酸素条件に対し呼吸量の低下は (1) のグループに比べゆるやかであるが, 呼吸量が抑制された後その呼吸量の抑制程度が実験終了時まで維持されたもの (コマツナ, レタス)。(3) 低酸素条件下におかれた後, 実験終了時まで呼吸量が減少し続けたもの (ブロッコリー, キャベツ) 。カリフラワー, レタスでは雰囲気中の酸素濃度と呼吸量の間には比例関係が認あられ, 酸素濃度10%条件下でも空気下に比べ呼吸量は明らかに減少した。しかし, その他の野菜では7%以上の酸素濃度条件下においては呼吸の抑制程度は小さく, 7%以下の酸素濃度域において酸素濃度の低下とともに明らかな呼吸量の減少がみられた。