Grapevine Structure and Function - Sonoma County

1 5 Grapevine Structure and FunctionEdward W. HellmanThis chapter presents an overview of Grapevine Structure and Function to provide abasic understanding of how grapevines grow. Such understanding is the foundationof good vineyard management, and the practical application of this knowledge isemphasized throughout this book. The reader should consult the references cited in this chapterfor more complete coverage of these topics. Much of the common viticultural terminology isintroduced in this StructureCells and TissuesThe basic unit of plant Structure and Function is thecell. All cells have the same general organization,consisting of a cell wall, protoplasm (liquid-filledregion containing living organelles), and the vacuole(region containing the cell sap).

2 This basic cellstructure is modified to create different cell types thatare capable of specialized functions . Organized groupsof specialized cells that perform specific functions arecalled tissues. For example, the outside protective skin of grape leaves, the epidermis, consists of oneto several layers of specialized cells. A thoroughdiscussion of the cell and tissue anatomy of grapevineshas been prepared by Pratt (1974), or a generaldiscussion of plant anatomy can be found in anyintroductory botany plant cells, termed meristematic cells, performthe specialized Function of growth by the creation ofnew cells through cell division. Groups of these cellsare organized into meristems (or growing points),positioned at various locations on the vine.

3 The apicalmeristem is a tiny growing point, hidden from viewwithin the unfolding leaves at the tip of an expandingshoot. In addition to the apical meristem, the shootproduces many additional growing points at the baseof each leaf, called buds; these are described in moredetail below. Each root tip also contains a growingpoint. Two specialized meristems, the vascularcambium and the cork cambium, are responsible forthe radial growth (diameter increase) of woody partsof the xylem and phloem tissues (described belowunder Vascular System) are produced every year froma specialized meristem called the vascular cambium(or simply cambium). The location and arrangementof cambium, xylem, and phloem vary between plantparts ( , shoots and roots) and with the develop-mental stage of the part.

4 The cambium consists of asingle layer of meristematic cells, which producexylem cells to the inside and phloem cells outside(Figure 1). Thus, the annual increase in girth of woodytissues such as the trunk is a result of the addition ofnew xylem and phloem cells from the cells are larger and produced in much greaterabundance than phloem cells, which form tissue onlya few cell layers thick. This causes the cambium alwaysto be positioned close to the outer surface of a woodystem. Older xylem can remain functional for up toseven years, but is mostly inactivated after two or threeyears. Some phloem cells continue to Function forthree to four exterior of woody parts of the vine is protectedby periderm, which comprises cork cells and is coveredby an outer bark consisting of dead tissues.

5 Once ayear, some of the cells within the outer, nonfunctionalphloem become meristematic, creating the corkcambium. The cork cambium produces a layer of newcells that soon become impregnated with an imper-meable substance, cutting off the water supply to thecork cells and older phloem that are external to thelayer. These cells die and add to the layers of bark cracks from the expansion growth of newbark beneath it, creating the peeling bark that ischaracteristic of older wood on 1. Cross section of 3-year-old Grapevine from Esau (1948) by Scott (Bark)PhloemVascularCambiumXylemAnnualRi ngRay6 Oregon ViticultureVascular SystemThe interior of all the plant parts described belowcontains groups of specialized cells organized into avascular system that conducts water and dissolvedsolids throughout the vine.

6 There are two principalparts to the vascular system: xylem is the conductingsystem that transports water and dissolved nutrientsabsorbed by the roots to the rest of the vine, andphloem is the food-conducting system that transportsthe products of photosynthesis from leaves to otherparts of the vine. The xylem and phloem tissues eachconsist of several different types of cells, some of whichcreate a continuous conduit throughout the plant, andothers provide support functions to the conductingcells, such as the storage of food products in xylemcells. A group of specialized cells are arranged innarrow bands of tissue called rays, which extend outTrunkCordonArmFruitingSpurShootDorman t SeasonGrowing SeasonRootSystemCrownFigure 2. Grapevine structures andfeatures: self-rooted vine.

7 Drawingby Scott from the center of a stem, through thexylem and phloem. Ray cells facilitate the radialtransfer of water and dissolved substances betweenand among xylem and phloem cells and are a site forstorage of food reserves. The vascular system con-stitutes the wood of older stems, and the thick cellwalls of the xylem provide the principal structuralsupport for all plant of the VineThe shape of a cultivated Grapevine is created bypruning and training the vine into a specific arrange-ment of parts according to one of many trainingsystems. Over the centuries, innumerable trainingsystems have been developed and modified in effortsto facilitate vine management and provide a favorablegrowing environment for the production of Structure and Function 7 Figures 2 and 3 illustrate a mature Grapevine as it mightappear at two representative time periods, trained totwo different systems.

8 The parts of the vine are labeledwith commonly used viticultural terms that oftenreflect how we manage the vine rather than describingdistinct morphological structures as defined Root SystemIn addition to anchoring the vine, roots absorb waterand nutrients, store carbohydrates, other foods, andnutrients for the vine s future use, and producehormones that control plant functions . The rootsystem of a mature Grapevine consists of a woodyframework of older roots (Richards, 1983) from whichpermanent roots arise and grow either horizontally orvertically. These roots are typically multi-branching,producing lateral roots that can further branch intosmaller lateral roots. Lateral roots produce manyshort, fine roots, which has the effect of increasing thearea of soil exploited.

9 Certain soil fungi, mycorrhizae,live in a natural, mutually beneficial association withgrape roots. Mycorrhizae influence Grapevine nut-rition and growth and have been shown to increasethe uptake of majority of the Grapevine root system is usuallyreported to be within the top 3 feet of the soil, althoughindividual roots can grow much deeper underfavorable soil conditions. Distribution of roots isinfluenced by soil characteristics, the presence ofhardpans or other impermeable layers, the rootstockvariety (see below), and cultural practices such as thetype of irrigation can be grown naturally on their ownroot system (own-rooted or self-rooted vines) or theymay be grafted onto a rootstock. A grafted vine (Figure3) consists of two general parts, the scion variety ( ,Pinot noir), which produces the fruit, and the rootstockvariety (often denoted by numbers, , 101-14),which provides the root system and lower part of thetrunk.

10 The position on the trunk where the twovarieties were joined by grafting and subsequentlygrew together is called the graft union. Successfulhealing of the graft union requires that the vascularcambiums of the stock and scion be in contact witheach other, since these are the only tissues having themeristematic activity necessary for the production ofnew cells to complete the graft union. Healing of thegraft union often results in the production of abundantcallus (a wound healing tissue composed of large thin-walled cells that develop in response to injury) tissue,often making the area somewhat larger than adjacentparts of the trunk. Because rootstock and scionvarieties may grow at different rates, trunk diametercan vary above and below the graft varieties were developed primarily toprovide a root system for Vitis vinifera L.