Sulfite Oxidase Activity Level Determines the Sulfite Toxicity Effect in Leaves and Fruits of Tomato Plants

Umanath Sharma,Aizat Bekturova,Moshe Sagi,Yvonne Ventura

doi:10.3390/agronomy10050694

Umanath Sharma, Aizat Bekturova + Show 2 more

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https://doi.org/10.3390/agronomy10050694

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Abstract

Increasing plant tolerance to sulfites/SO2 can lead to the development of tolerant crops to biotic and abiotic stresses. Plant sulfite oxidase (SO) is a molybdo-enzyme that oxidizes excess SO2/sulfite into non-toxic sulfate. The effect of toxic sulfite on leaves and fruits was studied in tomato plants with different SO expression: wild-type, SO overexpression (OE) and SO RNA interference (Ri). Sulfite-dipped ripe-fruits and sulfite treated leaf discs of Ri plants impaired in SO activity were more susceptible, whereas OE plants were more resistant, as revealed by remaining chlorophyll and tissue damage levels. Application of molybdenum further enhanced the tolerance of leaf discs to sulfite by enhancing SO activity in OE lines, but not in wild-type or Ri plants. Notably, incubation with tungsten, the molybdenum antagonist, overturned the effect of molybdenum spray in OE plants, revealed by remaining chlorophyll content and SO activity. The results indicate that SO in tomato leaves and ripe fruits determines the resistance to sulfite and the application of molybdenum enhances sulfite resistance in OE plants by increasing SO activity. Overall, the results suggest that SO overexpression can be employed, with or without molybdenum application, for developing fruit and vegetable crops tolerant to sulfite/SO2 containing pre- and postharvest treatments.

Highlights

Sulfur is the least abundant macronutrient in plants, comprising approximately 0.1% of the dry matter
The results show that the remaining chlorophyll content in the leaf discs after sulfite treatment was higher for the tomato lines with higher sulfite oxidase (SO) expression levels and lower 3for
The results show that the remaining chlorophyll content in the leaf discs after sulfite treatment was higher for the tomato lines with higher SO expression levels and lower for those with lower or no SO expression

Summary

Introduction

Sulfur is the least abundant macronutrient in plants, comprising approximately 0.1% of the dry matter. Sulfate (SO4 2− ) is the primary source of sulfur in plants [3,4]. The reduction of sulfate by the sulfate reduction pathway into cysteine is initiated by its adenylation catalyzed by ATP sulfurylase (ATPS) in both chloroplast and cytosol. In the primary sulfate assimilation, APS is first reduced by APS reductase (APR) to sulfite, which is further reduced to sulfide by the chloroplast-localized, ferredoxin-dependent sulfite reductase (SiR) [7,8,9]. The O-Acetyl-L-serine (OAS) synthesized from serine and acetyl-Coenzyme A catalyzed by serine acetyltransferase (SAT) together with sulfide is catalyzed into cysteine by OAS (thiol) lyase (OASTL) [9]

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