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emmagreen1220-blog · 7 years ago

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New Post has been published on Biology Dictionary

New Post has been published on https://biologydictionary.net/pollen/

Pollen

Pollen Definition

Pollen refers to the powdery product synthesized by seed plants responsible for the production of the male gametes of the plant (shown below).

The pollen grains are termed microgameteophytes, and consist of a sporopollenin coating which serves to protect the gameteophytes as they are transported from the stamens (male) or male cone to the pistil (female) or female cone in flowering and coniferous plants, respectively. When the pollen reaches the pistil or female cone, a pollen tube is formed, which transports the sperm to the ovule containing the female gametophyte. The term pollination refers to the transfer of pollen grains from the anther to the stigma of a flower. Cross-pollination involves the transfer of pollen from one flower to the stigma of another flower. In contrast, self-pollination involves the transfer of pollen from one flower to the stigma of the same flower. A diagram illustrating the location of the anther and stigma is shown below.

Pollen Structure

Pollen grains vary in size, shape, and surface characteristics depending on the plant species (shown below). In general, pollen grains have a double wall consisting of a thin inner wall composed of cellulose, termed the endospore, and a thick outer wall comprised of sporopollenin, termed the exospore. The shape and the external features of the exospore are highly variable, and are often used to distinguish pollen grain produced by different species. The purpose of this structure is to protect the male genetic material from the environment (e.g., UV radiation, compression, and water) during the transportation from the anther to the stigma. The surface of the pollen grain also contains various waxes and proteins which help repel moisture and interact with the stigma, respectively. However, such protein structures on the surface of pollen are often recognized by immune cells and are the source of the allergic reactions to pollen observed in humans.

Pollen Formation

In coniferous plants, pollen is formed in the microsporangia of the male cone, whereas it is produced in the anthers of flowering plants (also termed angiosperms). Each microsporocyte is diploid and forms four haploid cells, termed microspores, via meiosis. This process is termed microsporogenesis. The four microspores then form the double wall of the pollen grain within a structure made of callose. During this process, the callose is digested by callase and the pollen grains are able to grow and complete the formation of the endospore and exospore. The diagram below illustrates the release of pollen grains from the callose structures.

Quiz

1. The transfer of pollen from the anther to the stigma of a flower is termed: A. Endoporation B. Germination C. Pollination D. Microsporogenesis

Answer to Question #1

C is correct. The term pollination refers to the transfer of pollen grains from the anther to the stigma of a flower. Cross-pollination involves the transfer of pollen from one flower to the stigma of another flower. In contrast, self-pollination involves the transfer of pollen from one flower to the stigma of the same flower.

2. The primary function of the exospore is: A. Pollination B. Protect the plant’s male genetic material C. Protect the plant’s female genetic material D. Endoporation

Answer to Question #2

B is correct. The exospore is the hard outer wall of the pollen grain, which serves to protect the male genetic material from UV radiation and other potential sources of damage.

References

Clarke A, Gleeson P, Harrison S, and Knox B. (1979). Cell Biology Pollen-stigma interactions: Identification and characterization of surface components with recognition potential. Proc. Nati. Acad. Sci.76(7):3358-3362.

Heberle-Bors E. (1985). In vitro haploid formation from pollen: a critical review. Theoretical and Applied Genetics. 71(3): 361-374.

Gullvag B. (1966). The fine structure of pollen grains and spores: a selective review from the last twenty years of research. Phytomorphology. 16: 211-27.

Ward M, Dick C, Gribel R, and Lowe A. (2005). To self, or not to self… A review of outcrossing and pollen-mediated gene flow in neotropical trees. Heredity.95(4): 246-54.

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ahmadsuyoko-blog · 7 years ago

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Orchids: Why Are They A Critical Subject to Conservation in Indonesia ?

Orchids are any plants that belong to a taxonomical unit known as family Orchidaceae. Orchids comprise about seven percent of all angiosperms and one of the largest family in the group (Pansarin and Pansarin, 2011). There are 26,972 species in this family (Stern, 2014). They are cosmopolitan species and can be found throughout the globe except in the frozen land of Arctic and Antartic. Based on this fact, orchids can grow in any type of habitats ranging from lowland savannah to mountainous forest. Orchids are very variable in habits. Some have erect bodies, some creeps, some have numerous leaves and some only have one. So, what is an orchid ? Or what are characteristics for any plant to be called an orchid ? There are several requirements for any plant to be classified in the family Orchidaceae, namely:

1. Most members have one fertile stamen. Few have two (Cypripedium, Paphiopedilum) and only one genus has three (Apostasia).

2. Stamens and pistil are partially or completely united. This structure is called as gymnostemium or column.

3. Median petal (one that is opposite fertile stamen) is greatly modified or unlike the other two and known as labellum (lip).

4. Buds of most members are born with labellum above column. Before they start to open and while opening, they twist resulting in reversed positions. In some slipper orchids, they flip over and result in the same like the others. This phenomenon is recognized as resupination.

5. Modified stigma, rostellum is associated with pollen transfer.

6. Pollen grains are borne in masses called pollinia.

7. Seeds are exceedingly small (circa 0.5*1 mm) and very numerous.

(Arditti, 1992)

Indonesia is an archipelagic country that means it consists of islands from large ones to small ones. Even Indonesia possesses some of largest islands in the world. Papua (with half of being the territory of New Guinea) and Borneo are respectively the second and the third largest island in the world after Greenland (the first) (World Atlas, 2015). Indonesia is also a mega biodiversity country. There are roughly about 5,000 species of native orchids in Indonesia making it the richest one in the Malesian region and even the world’s largest orchid bearing country (Heywood and Country, 2012). Then why are orchids a concern to conservation in Indonesia ? To be able to answer this question, we gotta see some of these facts.

1. The rate of deforestation in Indonesia is reaching out to the worrying number. Times and Guardian magazines reported that Indonesia had the largest rate of deforestation as of 2014 with 840,000 hectares of forest lost in 2012 compared to 460,000 ha loss in Brazil as they quoted from a study ended in 2012.

2. Orchid species just like other living organisms have different kind or mode of adaptation to the environment. This is true since every species (even individual) inhabit their own niche (in some way, they might be overlapping with one another). Let’s say every individual has their own microenvironment requirements (microenvironment is a condition or more accurately refers to the condition resulting from mixed different environment factors in which every individual or species suits specifically).

Forest deforestation and land conversion have contributed much to the loss of native species. When a tree is being felled, epiphytic orchids lose their habitat. They lose any living support (attachment to substrate i.e. tree bark) alongside with supplies of sunlight, humidity, and temperature. This develops even worse with orchid species adapted to the shady condition. Epiphytic orchids become an interesting topic to be discussed about epiphytism since most of the orchids are epiphytic (out of 19,128 orchid species, seventy-three percent or 13,951 orchid species are epiphytic (Lüttge, 2012). They have features like chlorophyllous roots specializing for photosynthesis and succulent thick leaves adapting to water scarcity (they couldn’t easily take up water since they are arboreal or hanging from their substrates so main source of water is from the air humidity or rain drops).

An indirect effect of deforestation to the existence of orchids is related to the light need. Orchids can be sun-loving like Arundina graminifolia and Spathoglottis plicata or shade-loving like Oncidium Goldiana and Cymbidium sinense (Hew and Yong, 2004). The effect seems to be small for well adapted or cosmopolitan orchids. But it’ll be larger or major for endemic species. Phalaenopsis and Paphiopedilum are genera in the family Orchidaceae known to be shade-loving (Fatt and Astley, 2012) and direct sunlight seems to retard their growth. Direct sunlight is a result of vegetation clearing (as deforestation or land conversion). Let’s acknowledge ourselves that members of the two genera that are native to Indonesia are Paphiopedilum intaniae, Paphiopedilum hookerae, Paphiopedilum victoria-mariae, Paphiopedilum liemianum (IUCN Red List, 2017), Paphiopedilum bougainvilleanum, Paphiopedilum chamberlainianum, Paphiopedilum praestans, Paphiopedilum superbiens, Paphiopedilum tonsum (Asiatic Green, 2009), Phalaenopsis borneensis, Phalaenopsis pantherina, Phalaenopsis viridis, Phalaenopsis amboinensis, Phalaenopsis fimbriata, Phalaenopsis floresensis, Phalaenopsis javanica, Phalaenopsis robinsonii, Phalaenopsis venosa, Phalaenopsis inscriptiosinensis, and Phalaenopsis celebensis (Chen, 2011).

We have many species of Paphiopedilum and Phalaenopsis that are endemic - so protection to these genera are a concern. As a matter of fact, Phalaenopsis amabilis or moon orchid is declared as Indonesian flower of charm (Bahasa: puspa pesona) – therefore, if we don’t wanna lose our identity, we gotta keep that natural heritage.

Another indirect effect of deforestation affecting the existence of orchid is the change of air humidity as a consequent of direct sun lighting. Alterations in environmental factor such as air humidity can be transductional. As the air gets warmer and drier, it will evaporate any water droplet existing in the soil particles and the atmosphere near the ground. When soil gets drier, it will reduce the chance of microorganisms to survive and thrive. On the other side, we acknowledge that microorganisms are very important to soil (micro)fauna benefitting in the degradation of organic matter that will be used by the holomycotrophic or saprophytic orchids. In another word, we could say that holomycotrophic orchids are heterotrophic. As the land clears, we rarely could find Stereosandras, Epipogia, or Didymoplexuses which grow mainly under the shade-covered humus (commonly one from bamboo leaves - so they are usually found near clumps of bamboo trees).

Based on the explanation and rationale above – orchid conservation and protection is the responsibility of all Indonesian citizens.

References:

Books:

Arditti, J. 1992. Fundamentals of Orchid Biology. John Wiley and Sons, Inc.. Hoboken: p. 55.

Chen, Hong-Hwa. 2011. Orchid Biotechnology II. World Scientific. Singapore: pp. 2-5.

Fatt, C. T. and D. Astley. 2012. The Essential Guide to Growing Orchids in the Tropics. Marshall Cavendish International Asia Pte Ltd. Singapore: p. 96.

Hew, C. S. and J. W. H. Yong. 2004. The Physiology of Tropical Orchids in Relation to the Industry. World Scientific. Singapore: p. 68.

Heywood, V. H. and P. W. Jackson (eds). 2012. Tropical Botanic Gardens: Their Role in Conservation and Development. Academic Press. Cambridge, USA: p. 303.

Lüttge, U. 2012. Vascular Plants as Epiphytes: Evolution and Ecophysiology. Springer Science & Business Media. Berlin: pp. 258-259.

Pansarin, E. R. and L. M. Pansarin (eds). 2011. The Family Orchidaceae in the Serra do Japi, São Paulo state, Brazil. Springer Science & Business Media. Berlin: p.7.

Stern, W. L. 2014. Orchidaceae. Oxford University Press. Oxford: p. 1.

Websites:

Asiatic Green. 2009. Orchids: Paphiopedilum. Accessed from https://www.asiaticgreen.com/orchids_paph.htm on June 16, 2017 at 16:41 GMT+7.

Hellmann, M. 2014. Indonesia Now Has the Highest Rate of Deforestation in the World. Accessed from http://time.com/2944030/indonesia-now-has-the-highest-rate-of-deforestation-in-the-world/ on June 15, 2017 at 15:42 GMT+7.

Rankou, H. 2015. Paphiopedilum hookerae. The IUCN Red List of Threatened Species 2015: e.T43320406A43327874. http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T43320406A43327874.en. Downloaded on June 16, 2017 at 21:01 GMT+7.

Rankou, H. 2015. Paphiopedilum intaniae. The IUCN Red List of Threatened Species 2015: e.T43320508A43327889. http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T43320508A43327889.en. Downloaded on June 16, 2017 at 20:59 GMT+7.

Rankou, H. 2015. Paphiopedilum liemianum. The IUCN Red List of Threatened Species 2015: e.T43321398A43327909. http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T43321398A43327909.en. Downloaded on June 16, 2017 at 21:02 GMT+7.

Rankou, H. 2015. Paphiopedilum victoria-mariae. The IUCN Red List of Threatened Species 2015: e.T43322404A43328019. http://dx.doi.org/10.2305/IUCN.UK.2015-2.RLTS.T43322404A43328019.en. Downloaded on June 16, 2017 at 21:01 GMT+7.

Vidal, J. 2014. Rate of deforestation in Indonesia overtakes Brazil, says study. Accessed from https://www.theguardian.com/environment/2014/jun/29/rate-of-deforestation-in-indonesia-overtakes-brazil-says-study on June 15, 2017 at 15:42 GMT+7.

World Atlas. 2015. Islands of The World: The Largest. Accessed from http://www.worldatlas.com/aatlas/infopage/islands.htm on June 15, 2017 at 17:04 GMT+7.

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