Research article Flowers regulate the growth and vascular development of the inflorescence rachis in Vitis vinifera L. Aude M. Gourieroux a, b , Margaret E. McCully c, d , Bruno P. Holzapfel a, e , Geoffrey R. Scollary a, f , Suzy Y. Rogiers a, e, * a National Wine and Grape Industry Centre, Wagga Wagga, NSW, Australia b Faculty of Science, Charles Sturt University, Wagga Wagga, NSW, Australia c Division of Plant Industry, CSIRO, Canberra, Australia d Plant Science Division, Research School of Biology, The Australian National University, Canberra, Australia e NSW Department of Primary Industries, Wagga Wagga, NSW, Australia f School of Chemistry, The University of Melbourne, Melbourne, Vic, Australia article info Article history: Received 13 July 2016 Received in revised form 25 August 2016 Accepted 26 August 2016 Available online 28 August 2016 Keywords: Bunchstem Cluster Flower removal Grapevine Rachis development Vascular system abstract The rachis, the structural framework of the grapevine (Vitis vinifera L.) inflorescence (and subsequent bunch), consists of a main axis and one or more orders of lateral branches with the flower-bearing pedicels at their fine tips. The rachis is crucial both for support, and transport from the shoot. Earlier suggestions that the flowers per se affect normal rachis development are investigated further in this study. Different percentages (0, 25, 50, 75 or 100) of flowers were removed manually one week before anthesis on field-grown vines. Treatment effects on subsequent rachis development (curvature, vitality, anatomy, starch deposit) were assessed. Sections, both fixed and embedded, and fresh hand-cut were observed by fluorescence and bright-field optics after appropriate staining. Emphasis was on measure- ment of changes in cross-sectional area of secondary xylem and phloem, and on maturation of fibres and periderm. Specific defects in rachis development were dependent on the percent and location of flower removal one week prior to anthesis. The rachises curved inwards where most of the flowers were removed. When fully de-flowered, they became progressively necrotic from the laterals back to the primary axes and from the distal to the proximal end of those axes, with a concurrent disorganisation of their anatomy. A few remaining groups of flowers prevented desiccation and abscission of the rachis axes proximal to the group, but not distally. Flower removal (50%) reduced rachis elongation, while 75% removal reduced xylem and phloem area and delayed phloem fibre and periderm development. 75% flower removal did not affect starch present in the rachis during berry development. Developing flowers affect the growth and vitality of the rachis and the development of its vascular and support structures. The extent of these effects depends on the cultivar and the number and position of flowers remaining after some are removed one week before anthesis. © 2016 Elsevier Masson SAS. All rights reserved. 1. Introduction Grapevine (Vitis vinifera L.) inflorescences are compact panicles. They can have a variety of shapes and sizes depending on species, cultivar, percentage fruit-set, environmental factors and plant vigour. The structural framework of an inflorescence (and bunch) is the rachis, the proximal end of which (the peduncle) joins the shoot (Fig. 1). The rachis (also termed bunchstem) forks at the wing node to form two unequal branches (Bugnon, 1953), the shorter wing and the longer portion that subtends the main bunch. The primary axes form lateral branches which may ramify further. Each fine branch ends at the pedicels which support the flowers and berries. The vitality of the rachis is crucial to the development of berries and final yield (Hall et al., 2011) since it provides structural support and its vascular system forms the pathway for water and nutrient flow from the vine to the developing flowers and berries. Rachis development can be divided into two phases. The rachis lengthens rapidly early in the season, concomitant with shoot elongation, * Corresponding author. NSW Department of Primary Industries, Wagga Wagga, NSW, Australia. E-mail address: suzy.rogiers@dpi.nsw.gov.au (S.Y. Rogiers). Contents lists available at ScienceDirect Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy http://dx.doi.org/10.1016/j.plaphy.2016.08.016 0981-9428/© 2016 Elsevier Masson SAS. All rights reserved. Plant Physiology and Biochemistry 108 (2016) 519e529