PGs has revolved around the role of PGs in the fruit ripening process, pollen, and abscission. Pectin is one of the three polysaccharides present in the plant cell wall, and it plays a role in maintaining the barrier between the inside and outside environment and gives strength to the plant cell walls. Specifically, pectin in the middle lamella holds neighboring cells together. Fruit ripening The first GM food available in stores was a genetically modified tomato (also known as Flavr Savr) that had a longer shelf life and was ideal for shipping. Its delayed ripening was achieved by preventing polygalacturonase from destroying pectin, which makes tomatoes firm. An antisense PG gene was introduced, preventing polygalacturonase from ripening and softening the tomato. Although this method has been shown to reduce PG enzymatic activity by 70 to 90%, the PG antisense RNA did not hinder normal color development. Depolymerization of pectin is largely involved in the later stages of fruit ripening, especially as the fruit becomes overripe. While tomatoes are the prime example of high PG activity, this enzyme is also very active in avocado and peach ripening. PG enzymes in peach, two exo-PGs and one endo-PG, become active when the fruit is already soft. Fruits like persimmons may either lack PG enzymes or have very low levels of PG and as such they have not been detected yet. In these cases, other enzymes may catalyze the ripening process. Pollen Exo-PGs play a role in enabling pollen tube elongation since pectin rearrangement is necessary for the growth of pollen tubes. This PG activity has been found in grasses like maize as well as in trees, particularly in the Eastern cottonwood. Exo-PGs involved in pollen tube growth need Ca2+ for maximal enzymatic activity and can be inhibited by high concentrations of NaCl, citrate, and EDTA. Abscission zones It is largely unclear whether PGs play a role in facilitating abscission in certain plants, and if they do, whether they are exo- or endo-acting. Conflicting research has been published on, for example, whether PG is involved in citrus fruit abscission. One particular issue has been the usage of assays that are not able to measure exo-PG activity. An additional complication is the difference in PG enzymatic activity between fruit and leaf cell-separation zones. In peach, PG activity was only detected in fruit abscission zones. Other Agricultural pests like Lygus hesperus damage cotton and other crops