The Micronutrients & Plant Growth - Boron's Role
Boron (B) is an enzyme activator and is involved in the production of starch required for production of cellulose. The major function of boron is in sugar transport to meristem regions of roots and tops. This is manifested by the fact that transport of sugars is retarded in boron-deficient plants, resulting in reduced growth. Boron is also thought to be involved in cell formation and development; nitrogen metabolism; flower fertilization; active salt absorption; hormone, fat, and phosphorus metabolism; and photosynthesis. However, the general consensus is that all of these metabolic processes benefit directly from the influence of boron in sugar transport throughout the plant.
The first visible symptom of boron deficiency is death of the growing tips. This disorder is generally followed by growth of lateral shoots, the tips of which may also be deformed or die. The leaves of boron-deficient plants are usually thick, have a coppery texture, and become curled and brittle. Other symptoms include stunted roots, failure to set flowers, or flower abortion.
Boron deficiency causes internal tissues to disintegrate, causing abnormalities such as distorted, cracked, or hollow stems. Some crops exhibit specific symptoms. Beets, turnips, and potatoes exhibit poor tuber development. Apples have cork spot. Grapes form mixed clusters of small and large fruit, known as "hen and chicks", Cotton leaves become thick and leathery with abnormally long spongy petioles. The shorter leaf petioles are often twisted and have small ruptures along the stem. The fruit and leaves exude a sticky substance. Flower buds become Chlorotic with flared bracts. The squares and bowls dry up and often abort. Bolls that survive generally are deformed, are smaller in size, and fail to open fully. Soil analysis does not measure levels of boron because no reliable tests are available. However, a report may recommend applying boron for crops that are known to respond to it, such as alfalfa, apple, cotton, peanut, sweet potato, and several vegetables and flower crops.