MadSci Network: Botany

Re: Do telomeres also functions as biological clock in plants?

Date: Sat Apr 20 20:43:37 2002
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1019176591.Bt

The telomere biological clock hypothesis states that telomere length is reduced 
every time a cell divides and eventually gets too short for normal cell 
division. In some tissues, the enzyme telomerase can repair the telomere and 
prevent cell aging. 

Asexual reproduction is very widespread in the plant kingdom and often a very 
important method of reproduction for a plant species. Therefore, it may be 
that, unlike animals, plants normally have telomerase in all their meristems, 
which is where cell division occurs. Some plants are like people in the sense 
that they have a programmed life cycle of limited duration. Annual plants live 
one growing season, and biennials live two. Perennial plants, especially 
nonwoody perennials, often seem to have their life cycle ended not by their 
programming but by one or more environmental factor(s), such as drought, flood, 
wind storm, ice storm, cold temperature, pollution, disease, pest, mineral 
deficiency, competition from other plants, etc.

Perennial plants are designed to produce new organs, such as leaves, stems, 
roots, and flowers, every year. People are designed very differently. We have 
one set of organs, such as heart, lungs, eyes and brain, and parts such as arms 
and legs, for life. We can repair them to some extent but not make new ones. If 
we lose an arm, we cannot regenerate it. However, plants can replace lost 
branches. Each year, deciduous trees replace all their leaves, add a new layer 
of conducting tissue throughout their roots and stems, grow some new roots and 
stems, and usually make new reproductive organs (flowers or cones).    

The first and second websites, dated March 2001, cast doubt on telomeres and 
telomerase playing as key a role in plant aging as in animal aging. Annual 
Arabidopsis plants were altered to eliminate telomerase and followed through 
ten generations. Detrimental effects appeared in the sixth generation but the 
plants kept living and their cells kept dividing. They concluded that plants 
are fundamentally different than animals because plant cells can tolerate loss 
of telomeres and animal cells cannot. Much research remains to be done because 
Arabidopsis is just one plant species and an annual species at that.   

Some plants, such as redwoods and bristlecone pine, may live thousands of 
years, so their lifespans are much greater than for animals. Theoretically, a 
plant clone can be asexually propagated forever. Certain asexually-propagated 
plant clones have been in cultivation for at least hundreds of years. A male 
quaking aspen clone, called Pando, is thought to be as much as a million years 
old. It covers 48 hectares in Utah and consists of 47,000 individual trunks 
connected by a single root system. It spreads by root suckering. There is 
currently no way to tell the true age of plant clones that are efficient at 
asexually propagating themselves. Even individual clones of asexually 
reproducing nonwoody plants, such as dandelions, ferns, or mosses, may have 
originated thousands or millions of years ago. 

In many cases, rooting of cuttings actually results in a more juvenile plant 
than the parent because juvenile parts of the plant root more easily. Shoots at 
the base of a tree are the most juvenile. Unlike mature plants, juvenile plants 
cannot produce sex organs. Juvenile plants sometimes have a different 
appearance than mature plants. For example, juvenile English ivy (Hedera helix) 
is a vine with lobed leaves. Mature English ivy is a shrub with unlobed leaves. 

Some grasses are perennial but many are annual, such as wheat, corn, rice, 
oats, crabgrass, foxtails, annual bluegrass, barnyardgrass and annual ryegrass. 
Annual grasses use mainly sexual reproduction. Perennial grasses can use both 
sexual and asexual reproduction. 

Many perennial grasses spread via stolons or rhizomes. Rhizomes are below 
ground horizontal stems. Stolons are aboveground horizontal stems also called 
runners. Some grasses, such as Kentucky bluegrass also clone themselves using 
asexual seeds, a process called apomixis. Dandelions are also apomictic. There 
is tremendous interest in developing apomictic varieties of seed-propagated 
crop plants, such as grains and vegetables, because apomixis simplifies hybrid 
seed production.


Arabidopsis can survive the loss of an enzyme that prevents aging

A&M researchers hopeful a plant will lead to treatment of cancer, aging

Ancient Bristlecone Pine

Re: Will successive plant clones show genetic degradation?

Re: What are some good things and bad things about plant cloning?

What is apomixis?

Kentucky bluegrass apomixis

Scientists Announce a Breakthrough in Research on "Asexual" Maize

With its key role in plant maturation, a newfound gene could yield a novel 
class of genetically modified crops

Mitton, J.B. and Grant, M.C. 1996. Genetic variation and natural history of 
quaking aspen. BioScience 46: 25-31.

Pando clone of quaking aspen

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