Sap transport proteins. Recent evidence indicates that mobile proteins and RNA are part of the plant's long-distance communication signaling system. Evidence also exists for the directed transport and sorting of macromolecules as they pass through plasmodesmata." A large number of insects of the order Hemiptera (the half-wings), feed directly on phloem sap, and make it the primary component of their diet. Phloem sap is "nutrient-rich compared with many other plant products and generally lacking in toxins and feeding deterrents, [yet] it is consumed as the dominant or sole diet by a very restricted range of animals". This apparent paradox is explained
Plant tissue culture will generally overgrow the tissue culture medium before there is significant growth of plant tissue. Some cultured tissues are slow in their growth. For them there would be two options: (i) Optimizing the culture medium; (ii) Culturing highly responsive tissues or varieties. Necrosis can spoil cultured tissues. Generally, plant varieties differ in susceptibility to tissue culture necrosis. Thus, by culturing highly responsive varieties (or tissues) it can be managed. Aerial (above soil) explants are also rich in undesirable microflora. However, they are more easily removed from the explant by gentle rinsing, and the remainder usually can be killed by surface