Phloem is like plant’s version of blood-it transports nutrients up and down the plant. Extra phloem is sent to the roots for storage. Force is generated at the source-where the nutrients are going (also by where they are coming from). Phloem forces are positive pressure. The destination generates pressure lower than source-all positive pressures, no tension. Phloem cells are much smaller and have thinner cell walls than xylem. The outer part of phloem gives structure-bundle sheath. The primary phloem is the first phloem-first formed. The secondary phloem is made after primary a d comes after vascular cambium. In between shoot meristem and root meristems are primary tissues, xylem and phloem differentiate after these points. In a tree, a new meristem differentiates in the trunk-this is the cambium which makes new cells (trees).
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Sieve cells are called this because the tubes act as one continuous cell and are a collection of sieve tube elements. They tend to look empty, have very prominent joints, are very long and don’t have a nucleus (like xylem, but are living cells). They don’t have a cytoskeleton, have very few organelles (probably no Golgi, plastids or lignin; some ER, few mitochondria, have plasma membrane). Companion cells, ordinary cells that feed sieve cells and keep them alive, are next to sieve cells. A ‘sieve plate’ is the wall in between each sieve cell. Sieve plates contain special clotting proteins and polysaccharides which should only be released when the phloem is damaged. They are like slime and are very prominent; these are phloem clots that stop the flow of nutrients if the phloem is damaged.
Gymnosperm phloem does not have sieve tubes, only single cells. Sieve plates are on the side of the cell-works like a network rather than a pipe. These are called sieve areas. It is not understood how this works because sieve areas are filled with endoplasmic reticulum which blocks flow. The presence of membranes would mean that there can’t be a bulk flow, but it doesn’t seem to be possible in gymnosperms.
The conclusion of the study was that soil temperatures at or above 23 degrees C inhibit root growth and respiration both long and short term in A. stolonifera,and the specific maintenance respiration rates of A. stoloniferawere significantly higher than A. scabraat higher temperatures. Increased soil temperatures actually caused A. scabrato thrive and it can survive higher temperatures. The original hypothesis was supported.
The purpose of this study was to determine how rising temperatures (due to climate change) are affecting root growth, plant survival, carbohydrate metabolism, and root respiration rate in environments where plants are very temperature sensitive, and to better understand how roots maintain growth and function under high soil temperature conditions. The hypothesis was that A. stoloniferawould have lower root respiration responses than A. scabraat higher temperatures.
It is important to understand how roots respond to temperature because it can affect root and relative growth rate, and in species with roots sensitive to temperature change, growth can be affected negatively. In this study, two species of grass were tested, one whose roots were more heat-sensitive and one whose roots were not. This was to see if species with heat sensitive roots would be affected greater than species whose roots are not heat sensitive. A. scabrais a known grass that thrives at very high soil temperatures, while A. stoloniferais a high-temperature sensitive grass grown in cool climates.
Fertilizer has been shown to reduce the production of volatile organic compounds. Pests tend to prefer plants with fewer volatile organic compounds, and plants treated with more than enough fertilizer are preferable to pests (Islam et al. 2017). Heavily fertilized soil has been associated with less chemical defense compounds in plant leaves (Prudic et al. 2005). Less volatile organic compounds and fewer chemical defenses encourage herbivore consumption. A well fertilized plant treated with jasmonic acid should be more desirable to an herbivore than a poorly fertilized plant treated the same.
However, artificially inducing plant defenses depletes energy and resources for other functions. It has been shown to consequently affect growth, reproductive processes, fruit and leaves (Redman et al. 2001; Koussevitzky et al. 2004). Treating plants with jasmonic acid has been shown to result in larger but fewer fruits and can alter amount of seeds produced and germination success (Redman et al. 2001). The treatment has been shown to increase the amount of polyphenol oxidase in chloroplasts (Koussevitzky et al. 2004). Excess polyphenol oxidase causes fruits and leaves to brown faster and the fruits to consist of more pigments, a sign of increased rate of cell death (Araji et al. 2014). Plants treated with jasmonic acid should be smaller than those not and show signs of poor health.
Mechanical damage by cutting leaves has shown less response in plant defenses than herbivore damage because enzymes released by herbivores trigger a greater response. Mechanical damage increases concentration of jasmonic acid less than herbivore damage (McCloud and Baldwin 1997). The amount of trichomes increases slightly with clipping leaves, but not like damage from herbivores (Björkman et al. 2008). Applying jasmonic acid has been shown to increase trichrome growth without damage from herbivores. Trichomes are hair-like defensive structures that grow on the leaves of plants that impede movement. Jasmonic acid induces creation of secondary defensive compounds that are less favorable to herbivores and impede herbivore growth (Tian et al. 2012). Mechanical damage with treatment of jasmonic acid may produce the best results for herbivore deterrence.
The reaction of plants to stress from their environment involves a series of pathways which induce defenses (Tian et al. 2014). These pathways involve several hormones which trigger the defense responses in plants. Jasmonates are stress-induced phytohormones that incorporate biotic and abiotic cues that regulate plant growth, development, and defense responses. Jasmonic acid is a hormone plants release to control the responses from herbivore consumption. While impeding growth, the application of jasmonic acid to plants has been shown to enhance the treated plant’s natural defenses (Huang et al. 2017).