Grapevine Biology I
The following topics are covered on this article:
• The main types of plant tissues (meristematic, dermal, photosynthetic, structural and vascular);
• Grapevine anatomy (roots, shoots, buds, leaves, flowering, fruit);
On the next blog article we are going to cover photosynthesis, translocation, transpiration and respiration vital processes.
Types of plant tissues
Growth (meristematic) tissue
Meristematic cells divide to make more cells, allowing the vine to grow. They occur in the buds, root tips and shoot tips (development of organs). The cambium layer of the vine shoot/cane is an example of a secondary meristem because it enables organs to grow in thickness.
Protection (dermal) cells
The cells of the epidermis are the outermost layer of cells on all plants. The bark protects the inner cells from physical damage.
Chloroplasts are sugar producing cells which are mainly found in the leaves. The chlorophyll in them enables photosynthesis to occur.
Support tissue which makes up the cortex
Collenchyma (living outer most layer) cells; form a complete cylinder around the stem. They are elongated and have thicker cell walls due to additional cellulose, deposited within their walls.
Sclerenchyma (support) cells; are similar to collenchyma cells but have additional lignin fibers in their cell walls. As these fibers mature and die they leave a hard skeleton of lignin fibers.
Parenchyma (storage) cells; are living cells which have large central vacuoles (storage vessels) and thin but flexible cell walls. They form the cortex and pith of stems, the cortex of roots and the mesophyll of leaves.
Vascular or conducting tissue
Xylem tissue conducts water and dissolved mineral salts. Perforations in cell walls facilitate the movement of water and dissolved substances from the roots upwards into the shoot system of the vine.
Phloem is the food or sugar conducting tissue located on the inside of the bark. Sugars are moved from the production site to a ‘sink’ or where it is to be utilized.
Root Distribution and Function
Young roots contain a root tip which is a region of rapidly dividing cells protected by a root cap. Behind this is the area of absorption of nutrients. The root apical meristem allows for extension growth. As the root develops, the epidermis dies and is replaced by the exodermis. This gives the root the brown color. Concentrically from the outside a root is formed by the epidermis, followed by the cortex (parenchyma cells), and the endodermis which contains the Casparian strip, a layer of cells with thickened cell walls that regulate solute transport (helping to protect vines from effects of soil toxicities).
Many new roots grow each year, some of which develop into main structural roots that support or anchor the vine. Most of the annual root growth dies in the same season.
2) Water and nutrient absorption
Dissolved nutrients in the soil solution are absorbed by feeder roots and diffuse into the vascular tissue (the xylem).
3) Storage of reserves
In late summer and autumn, some of the products of leaf photosynthesis (sugars) are transferred via the phloem tissue back to the root system and other woody parts of the vine providing carbohydrate reserves for the next season’s growth.
4) Hormone production
Hormone production (gibberellin/cytokinin) by the roots influences growth and development of the shoots and clusters of the grapevine.
A shoot is the succulent stem bearing the leaves, tendrils and flower clusters (inflorescences). All of the information required to grow a shoot is contained within a bud. Growth in length occurs via cell division at the shoot tip (in meristematic tissue) and by elongation of the newly formed cells.
In the developing grapevine, the leaves undergo a gradual transition from importing photosynthetic products to export. When the leaf is 1/3 its full size it exports more food than it uses and begins to contribute to vine growth. When the leaf reaches its full size (about 30 to 40 days after unfolding) it is photosynthesizing at its peak.
Following harvest/fruit removal, the majority of photosynthates are directed towards and stored in the roots. Leaf fall or senescence normally begins in late autumn when minerals are translocated (remobilized) back into the canes and trunk.
Buds may be classified into either a ‘prompt’ bud or a ‘compound’ bud.
The compound bud
The compound bud is comprised of the primary, secondary and tertiary latent buds. Each bud contains three partially developed shoots enclosed in small leaf like structures called bracts which develop in the leaf axil.
The Lateral Shoot and Prompt Bud
The summer lateral grows from a prompt bud in the leaf axil. It produces shoots and leaves in the current growing season and is usually not fruitful. Compound buds produce shoots, leaves and fruit after the completion of winter dormancy.
Formation of Grapevine
1. Anlagen; First anlagen form as club-shaped meristematic protuberances from the apices of latent buds. At this stage, the anlagen are uncommitted primordia; they may develop into inflorescence primordia, tendril primordia or shoot primordia.
2. Inflorescence primordia; The formation of inflorescence primordia takes place if the anlage undergoes repeated branching to develop many rounded branch primordia. This process is controlled by both environmental (temperature, light) and endogenous (growth regulator) factors.
3. Flower formation; Grapevine flowers are small (4-5 mm) and grouped together in a flower cluster or inflorescence. The inflorescences occur opposite a leaf in the same position as a tendril (there are several hundred flowers per inflorescence). Six to ten weeks after bud burst, flowering takes place.
Poor set may be characterised as Coulure, Millerendage and/or ‘Hen and Chicken’.
1) Coulure occurs when many flowers fail to develop into berries and drop (shatter) from the cluster within 10 days of opening.
2) Millerendage is a condition characterized by berries arrested at different stages of development and of different berry sizes on the same bunch. They may include but are not limited to live green ovaries (LGOs), chickens or a combination of both (resulting in a loose bunch).
3) Hen and Chicken is a condition where there are a high proportion of small, coloured and underutilized ‘chicken’ berries on a bunch.
Factors Affecting Berry-Set
Berry set is reduced by high temperatures during and immediately after flowering. Water stress at flowering and during the subsequent four weeks has been associated with poor set.
Berry growth stages
Stage 1: Rapid Growth (40 to 60 days) The seed increases in size. There is a rapid increase in berry size due to cell division in the first two weeks, and some expansion; the berry remains hard, acid is high and sugar levels almost constant.
Stage 2: A lag stage of nil or slow growth (7 to 40 days) The ‘lag phase’ is a period when either less growth or no growth in volume occurs. The boundary between stage 2 and 3 is often unclear.
Stage 3: Growth resumes and maturation begins (approx 35 to 55 days) The onset of Stage 3 is signalled by veraison, the point of sudden change in colour. During this stage, the berry softens, acid levels decrease, sugar is accumulated, varietal flavors and aromas develop. The rapid increase in berry volume is due to cell enlargement.
Source: GRAPEVINE BIOLOGY, Mary Retallack - Retallack Viticulture.
Leave a comment