Senescence it’s Retardation of

SenescenceCREATED BY : CHAVAN MAHADEV RAJARAM

COLLEGE OF AGRICULTURE , DAPOLIM.SC (AGRI)

Department of Agricultural Botany(GPB)

Senescence Life comprises of following sequential events germination/birth, juvenile state, maturation, old age and death.Old age called senescence in plants.Senescence biological process of deterioration with age.This stage leads to complete loss of organization and function and finally complete inhibition of life activity i.e. death, thus senescence is penultimate phase of life. But death is not part of senescence.Meristem don’t undergo senescence and are considred as potetially immortal.

Types of senescenceTop senescence :- occurs in aerial

parts of plant. Common in perennials. Deciduous senescence :- Occurs in

deciduous plants. Only occurs in leaves. Overall senescence :- seen in annual

plants. Senescence occurs orderly in flower, fruits, leaves and root.

Progressive senescence :- It is common in annual plants. First seen on old leaves and then new leaves.

Retardation of senescenceIt means that delay the

degradation of plant.Also increase the life of plant and

getting more and more yield.Delay the senescence of many

plant parts i.e. flowers, leaves and fruits.

This retardation of senescence with the help of many factor studied by many people these are as follows:

Inhibition of Leaf Senescence by Auto regulated Production of Cytokinin.

Controlling expression of IPT, a gene encoding isopentenyl transferase (the enzyme that catalyzes the rate-limiting step in cytokinin biosynthesis), with a senescence-specific promoter results in the suppression of leaf senescence.

Transgenic tobacco plants expressing this chimeric gene do not exhibit the developmental abnormalities usually associated with IPT expression because the system is autoregulatory. Because sufficient cytokinin is produced to retard senescence, the activity of the senescence-specific promoter is attenuated.

Senescence-retarded leaves exhibit a prolonged, photosynthetically active life-span. This result demonstrates that endogenously produced cytokinin can regulate senescence and provides a system to specifically manipulate the senescence program.

Retardation of Leaf Senescence by Ascorbic Acid

Leaf discs of Solatium melongena were floated on various concentrations of ascorbic acid (AA), gibberellic acid (GA3), and kinetin in order to study their effect on senescence.

AA was highly effective in retarding senescence as shown by the arrest of the fall in levels of chlorophyll, DNA, RNA, and proteins.

AA was effective at a lower concentration than that of GA3 or kinetin.

Retardation of leaf senescence by inhibitors of RNA and protein synthesis

Effects of actinomycin-D (ACT), cycloheximide (CH), rifampicin (RIF) and chloramphenicol (CAP) on senescence of soybean leaf discs were investigated.

All inhibitors tested are effective in retarding senescence of soybean leaf discs. However, CH is more effective than ACT, RIF and CAP, suggesting that activation of preexisting, latent metabolic systems present in the cytoplasm plays predominant role in the initiating of leaf senescence.

However, the possibility that events taking place in the nucleus or chloroplast are essential for the initiation of leaf senescence cannot be excluded.

Retardation of radish leaf senescence by polyamines.

The effect of polyamines and related metabolites on several parameters of leaf senescence was followed in detached radish (Raphanus sativus L. var. radicular cv. “Giant Butter”) leaves floated on test solutions in darkness.

Leaf senescence was accompanied by a marked loss of chlorophyll, which started at 24–48 h of incubation. The polyamines, spermine and spermidine, and the diamines, putrescine and cadaverine, were highly effective in arresting chlorophyll loss over a period of at least 96 h. L-arginine, and especially L-ornithine, were less active. Polyaminens prevented the marked chlorophyll loss in dark-incubated leaves, but did not compensate for the moderate chlorophyll loss when the leaves were aged in light.

Polyamines were also highly effective in retarding earlier events of leaf senescence, prior to chlorophyll loss: both protein degradation and ribonuclease activity were inhibited by spermidine.

Chlorophyll and protein loss in dark-or light-incubated suspensions of either “intact” or disrupted chloroplasts was not affected by polyamines. – It is concluded that polyamines are highly effective in preventing chlorophyll loss from detached leaves, possibly by controlling early senescence-linked events which occur in darkness rather than by direct inhibition of chlorophyll degradation.

Retardation of senescence by low temperature and benzyladenine(BA) in intact primary leaves of soybean.Effects of temperature and benzyladenine (BA) on the senescence of intact primary leaves of soybean were investigated.

Compared with high temperature (30°C for day and 25°C for night), low temperature (15°C for day and 13°C for night) significantly retarded senescence of intact primary leaves.

Repeated daily treatment of the primary leaves with BA (200 mg/liter) beginning 15 days after growth at high temperature resulted in retardation of the senescence process.

The lower activity of cytokinins in the primary leaves of seedlings grown under high temperature may be responsible for rapid senescence.

Retardation of Leaf Senescence in Maize by Subtoxic Levels of Bromacil, Fluometuron, and Atrazine

Soil applications of subtoxic dosages of three selected photosynthesis inhibitors caused marked retardation of senescence in the basal leaves of maize (Zea mays L, cultivar Cribfiller)

The observations were confirmed quantitatively by (a) spectrophotometric determination of relative chlorophyll content and (b) comparison of 14CO2 incorporation, in leaves from treated and control plants.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) and fluometuron (1,1-dimethyl-3-(α,α,$\a lpha$-trifluoro-m-tolyl) urea) exhibited pronounced activity, by both criteria, retarding senescence at 0. 030-0.090 ppmw and 0 150-0.750 ppmw in the soil, respectively.

Atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) produced a similar trend but at higher concentrations (0.300-0 900 ppmw).

The results obtained with bromacil and atrazine add to the literature two new chemical classes of compounds (uracils and triazines) which contain no purine ring yet exhibit one recognized cytokinin-like activity, retardation of senescence in intact plants.

From above discussed experiments we concluded that there are many factors responsible for retardation of senescence.

Mainly due to more secretion of cytokinin, auxin, GA3, polyamines and other growth retardent are retarded the senescence.

We all known about the Richmond-Lang Effect due to available of cytokinin.

Factors responsible for retardation of senescence.Plant harmones :- Auxin,

cytokinin, GA3, polyamines and other growth retardents.

Types of nutrients :- Calcium and Nitrogen application.

Availability of water/ irrigation.

Light :- opening of stomata in light time.

Temperture :- lower temp. Retard senescence.

Case study

Conclusion

ReferencesPlant Physiology - S. N. Pandey

and B. K.SinhaText book of Biology – Vaishali

patil-ShirureJournal of Plant Cell PhysiologyJournal Exp. BotanyInternet Wikipedia page

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