Pre-Anthesis Cytokinin Applications Increase Table Grape Berry Firmness by Modulating Cell Wall Polysaccharides.

Bárbara Rojas,Susana Saez-Aguayo,Romina Pedreschi,Joaquín Delgado-Rioseco,Bruno G Defilippi,Baltasar Zepeda,Claudio Meneses,Felipe Suárez-Vega,Alonso G Pérez-Donoso,Patricio Olmedo,Reinaldo Campos-Vargas

doi:10.3390/plants10122642

Abstract

The use of plant growth regulators (PGRs) is widespread in commercial table grape vineyards. The synthetic cytokinin CPPU is a PGR that is extensively used to obtain higher quality grapes. However, the effect of CPPU on berry firmness is not clear. The current study investigated the effects of pre-anthesis applications (BBCH15 and BBCH55 stages) of CPPU on ‘Thompson Seedless’ berry firmness at harvest through a combination of cytological, morphological, and biochemical analyses. Ovaries in CPPU-treated plants presented morphological changes related to cell division and cell wall modification at the anthesis stage (BBCH65). Moreover, immunofluorescence analysis with monoclonal antibodies 2F4 and LM15 against pectin and xyloglucan demonstrated that CPPU treatment resulted in cell wall modifications at anthesis. These early changes have major repercussions regarding the hemicellulose and pectin cell wall composition of mature fruits, and are associated with increased calcium content and a higher berry firmness at harvest.

Highlights

Grapevine (Vitis vinifera L.) is among the most valuable crops, with 80 million tons produced globally every year [1]
A previous work showed that CPPU applications at early stages of inflorescence development prevented postharvest disorders [17], suggesting that the BBCH15 growth stage—where inflorescence is clear and displays five separate leaves—and the BBCH55 growth stage—where flowers are in compact groups and display eight separate leaves— are key stages for CPPU application
Taken together, our results indicate that CPPU treatment prior to anthesis produces an effect at the cell wall level, as evidenced by differences at the morphological level of ovaries at anthesis and, in berry firmness at harvest

Summary

Introduction

Grapevine (Vitis vinifera L.) is among the most valuable crops, with 80 million tons produced globally every year [1]. Several traits are commercially significant for table grapes such as berry size, sugar content, and firmness [2,3,4] This crop has been accompanied by the use of plant growth regulators (PGRs) to sustain economically viable production and increase its commercial value [5]. The biological processes mentioned above are accompanied by endogenous hormonal changes, including high levels of gibberellic acid and cytokinin at early stages of fruit development that drive a rapid cell division and enlargement in grape berries [10], whose function is to carry out fruit set and the early growth, followed by tissue differentiation and fruit softening as a result of ripening when lower hormonal levels are reached [11]

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