Leaf discoloration

Leaf discoloration can be from cell death, or it can be from an interruption of plant biochemical processes as a result of nutrient deficiencies or environmental pollutants. 

Heavy metal ions such as Cu, Zn, Mn, Fe ", NP", and Co are essential micronu-tritients for plant metabolism. When these ions are not available to the roots, plants develop specific deficiency symptoms, though when present in excess, these - as well as nonessential metals such as Cd ", Hg " and Pb " " - can become extremely toxic. At high concentrations, all these metals may cause symptoms such as chlorosis and necrosis, stunting, leaf discoloration and inhibition of root growth (Marschner... 

Because of the toxicity associated with lead compounds, governmental rulings have severely limited the use of lead drier in coatings. From a performance viewpoint the use of lead in aluminum paint will destroy the leafing characteristics of the film. Coatings containing lead that are exposed to sulfur fumes will discolor. 

Tip-over of plants Discolors fruit Disfigures fruit Discolors green fruit Discolors green fruit Leaf damage Leaf damage Leaf damage Infects ripe fruit Vector of bunchy-top... 

Sapium sebiferum (L.) Roxb. S. discolor Mueller-Arg. Wu Jiu Shan Jiu (Chinese tallow tree, Chinese vegetable tallow) (Leaf, root bark) Xanthoxylin, corilagin, sebiferic acid, lauric acid, margaric acid, palmitic acid.33-50 Antihypertensive activity, for constipation, poisoning, skin diseases. 

The best method for evaluation of the color problem is to prepare a food product containing the protein flour. Biscuits were routinely used as the model food system. Figure 5 illustrates the color of biscuits prepared with lOOZ wheat flour and with 20Z plant-protein products. The color of the biscuits prepared with soybean and peanut flours shows that these ingredients do not cause a serious color problem. However, sunflower, alfalfa leaf, and cottonseed flours do produce a discoloration in this model food system. The L and b values generally reflect this visual evaluation. 

Flaky or leaf gum, perfectly white,... 40 to 60 Flaky or leaf gum, discolored or brown, IS to 25... 

When gum-tragacanth Is purchased for shipment to Europe, it undergoes the following assortment —The large, white, flaky, or leaf gum, formed French quality, is first picked out, and the residue is sifted. The coarser portion is returned to the pickers, who remove. the discolored leaf, which is termed English quality. The remainder is then examined, and any stones, or dirty, very black pieces ore thrown aside as refuse the rest, composed of naturally exuded gum and brown leaf, is denominated common or sorts. 

When the gums arc intended for the French market, the fine white leaf only is shipped the vermicelli is sold for Trieste, and the discolored leaf and sorts for England. 

Several studies have described a relationship between the activity of PAL in iceberg lettuce leaf tissue and the development of RS symptoms [141-146]. Hyodo et al. [141] observed that an ethylene-induced increase in PAL activity parallelled the appearance of RS symptoms. These researchers also measured an increase in total phenolic compounds. It has been proposed that ethylene induces PAL activity and the resulting accumulation of phenolic compounds in cells leads to their discoloration and eventual death [141,143,145]. 

Necrotic areas may appear on an otherwise normal appearing leaf, or they may be accompanied by varying degrees of yellow discoloration (chlorosis). Chlorosis may form a transition zone between completely dead and the healthy areas, or it may cover any portion of the living tissue. Chlorosis often develops in tissues which have accumulated an excessive but nonlethal amount of a particular toxicant. Various patterns and degrees of chlorosis occur when chlorophyll is attacked by the toxic pollutants. Characteristics of the chlorotic pattern are influenced by the sensitivity of plants exposed, type of pollutant, dosage received, and environmental conditions under which the plant is grown. 

Sulfur Dioxide. S02 injury on plants has received much attention, particularly during the past half century, and the toxic effects are well known. Symptoms of acute injury to specific crops have been described by investigators in several countries (2, 3, 4, 6, 7, 8, 15). Acute necrosis results from rapid absorption of S02. Once S02 enters the mesophyll tissue, it reacts with water to produce the sulfite ion which has strong phytotoxic properties. When lethal concentrations accumulate in the most susceptible areas of the leaf, a dark green, water-soaked discoloration develops. The affected area soon becomes flaccid, and upon drying becomes white to ivory on most plants. In some instances the dead tissue may turn red, brown, or almost black. 

One of the earliest indications of ozone injury on several plant species is an upper surface discoloration with a waxy appearance. This symptom often disappears completely a few hours after exposure is terminated. High dosages of ozone cause permanent necrotic lesions on susceptible leaf tissue. Permeability of cell membranes is apparently disrupted, and cell contents are allowed to leak into the intercellular spaces producing a water-soaked appearance. Upon drying, the tissue will totally collapse and turn white or various shades of brown. Lesions which extend through the entire thickness of the leaf are commonly referred to as bifacial... 

NATURE OF DAMAGE. The upper side of the leaf has a speckled, pale and dull appearance as a result of sucking by the mites. The underside of the leaf has a brownish discoloration. More severely affected leaves become silvery and can eventually turn brown. They then curl up from the edge inwards. 

TCA, the sodinm salt of trichloroacetic acid, is primarily employed to control monocotyledons. Uptake of the highly water-solnble trichloroacetate takes place mainly via the roots or rhizomes. The active snbstance is concentrated in the growth-active areas, and symptoms of wilting, dark green discoloration, or even of leaf deformation may occur. The plants finally begin to die after several days. 

Willow lace bug adults and larvae also feed on willow leaves, causing severe discoloration. These A - A" pests have distinctive lacy wings and commonly feed on the undersides of leaves. Control by spraying upper and lower leaf surfaces with insecticidal soap. 

Leaves yellow and wilt. Cause Root rot. Root rots are caused by various species of fungi. Besides the common leaf symptoms, root rots can also cause reduced growth, branch dieback, and the ultimate death of the plant. At the soil level, the stem wood may be discolored. or stringlike fungal structures may be present. Yellow-orange mushrooms sometimes appear at the base of dying trees. Remove infected trees as soon as possible to reduce the spread of the fungus to other trees. 

Symptoms Infection by wilt fungi cause leaves to yellow and leaf stems to droop, giving plants a wilted appearance. The yellow leaf patches turn brown and may spread to cover whole leaves. Leaves often fall early, and plants will die. Symptoms usually first appear on the lower or outer parts of plants. The interior of the stem near the base may be discolored (see photograph of stem damage on page 396). 

Discolored patches on leaves may be signs of the pathogen. For example, the white powdery covering of powdery mildew is actually the fungus spreading across leaf surfaces. 

Symptoms This virus often produces stunting by causing trees to grow shoots that have abnormally short distances between the leaf nodes. Leaves may be discolored. The tree usually dies within a few months. 

In aquatic plants adverse effects of mercury such as senescence, growth inhibition, decreased chlorophyll, protein and RNA content, inhibited catalase and protease activities, inhibited and abnormal mitotic activity, increased free amino acid content, discoloration of floating leaves, leaf and root necrosis, and death have been reported (Muramoto and Oki 1984, Mhatre and Cha-phekar 1985, Sarkar and Jana 1986). The level of mercury that results in toxic effects in aquatic plants varies greatly. Freshwater concentrations of between 50 and 3400 pg Hg " " or 0.8 to 6 pg methyl-mercury are toxic to plants, and for salt water 10 pg Hg " " for algae and 160 pg Hg " for seaweed are reported. No data are available on methylmercury in saltwater plants (EPA 1997). 

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