·If fungi require 2 different strains mycelium to form zygospores
it is called heterothallic fungi.
Is
all fungi are heterothallic
·No,
there are basically 2 types of fungi.one heterothallic that needs different
nature mycelium to produce zygospore.
·Andanother is homothallic that do not need
different nature mycelium.
·The
mycelium developed from single spore are compatible for each other.
·They
can make zygospores on hyphae of a single mycelium.
About
heterothallic fungi
·The
2 different mycelium are morphological similar but physiological and sexual
different.
·The
term + and – for two type of strains.
History
·While
studying mucorales- Blakeslee found that some species develop zygospores
Independtly ,whereas some (like m.mucedo)produce zygospores in the presence of
mass of mycelium.
·The
2 mycellium of mucedo arising from different spores are nessery for the
production of zygosporesand also different
in strains.
·These
mycelium were morphological similar but not physiological and sexual.
Further,
Work on heterothallism and homothallism by
raper proved there is
“no absolute
separation of sex”
4type of mycellim in achlya bisexualis
are found by them-
1-Pure male
2-predominetly male(can make oogonia)
3-Pure female
4-Predominantly female ( can make
antherdia)
5-But none of them able to make
zygospores alone.
·Each
needs one of three .
·These
type of heterothallism called- gynandromictic.
Hormones
·These
are some chemical that govern sexual process that are called hormones.
·Raper
named them A, B, C, D.
·One
of them is sirenin that is isolated from allomyces .
·Sirenin
is responsible to attract male gametes.
Type of heterothallism
1-morphological heterothallism
2- Physiological heterothallism
Morphological heterothallism
·When
one can distinguish the male and female sex organ by its structure or
morphology.
Physiological
heterothallism
·Reproduction
place by physiological different hyphae.
·Also
known as haploid incompatibility.
They
are two types 1.2 allele 2.Multiple allele
2
allele heterothallism
·Nucleiof both mating types are genetically
different.
·Sexual
compatibility is controlled by genetic factor. “A” , “a”.
·Both
factors are present in different chromatid of chromosomes.
·Due
to dominance of “A” over “a” they also represented by “+” and “-“.
·At
meoisi they got seprate with chromatid.
·Spores
formed with on “+” allele and another spore formed of“–“ allele.
·Spore
with + allele give rise to + mycelium and – to – mycelium.
• throughout the temperate and tropical regions and even in Arctic zone
•in India mostly found in hilly areas very few species grow in Plains like cycadales.
•Living gymnosperm are perineal xerophytic, Woody evergreen plant none of them are annual.
External features
• plant body is sporophytic and differentiated into root, leaf & stem
• the gymnosperm sequoia world tallest tree ( the giant Redwood) 125 M height and 30 M with 4000 year old in Redwood Park( California)
• smallest gymnosperm Zamia with underground tuberous stem .
•Tap root system, sometimes symbiotic relationship with algae and fungi found
• in cycas root show symbiotic relationship with algae
• in pinus root show symbiotic relationship with fungi.
•stem usually erect profusely branched( unbranched in cycas) tuberous in zamia
•Leave scars on stem are characteristic feature of gymnosperms.
•the arrangement of leaves is spiral on stem or cyclic in some gymnosperm. The foliage of leaves of some coniferous are modified into long needles.
•Leaves maybe monomorphic( that is one kind leaves) and dimorphic (that is of two kind of leaves)
• in dimorphic, the foliage leaves are evergreen and protected by the cuticle whereas the scale leaves a minute and dioecious.
Internal feature
• the vascular cylinder of roots maybe diarch or polyarch
• stem possess Collateral endarch and open vascular bundle arranged in ring
•secondary growth occurs. secondary growth of occur by the activity of cambium
•xylem cosist of only tracheids and xylem parenchyma.vessels are absent (gnetals except).
•Phloem have sieve tube &phloem parenchyma but companion cells are absent.
•Stem show distinct secondary growth
•Woods are manoxylic type in cycas
•Pycnoxylic in pinus
•Leaves -Mesophyll of leaf is undifferentiated or differentiated into palisade and spongy parenchyma.
•Stomata are sunken.
•Most of the gymnospermic leaves do not have ventral veins and translocation of nutirents take place by transfusion tissue.
Reproduction
•Cones are usually monosporangiated but (ephedra species) are bisporangiated.
•Male microsporangia develop on abaxial side of micro sporophyll.
•Eusporangiate
•Megasporophyll may be similar to foliage leaves or cauline(pinus).
•Ovular integument have 3 parts-outer layer and inner layer is flashy but middle layer is stony.
• heterosporous plant usually produce two different type of spores microspheres that is male megaspore that is female spores are found in sporangium.
•The microsporangium are born on lower surface of microsporophyll and megasporangium are born naked on megasporophyll
• microsporangium maybe arrange indefinite group called sori their number may be reduced to 2 in pinus
• microsporophyll are aggregated in a form of compact structure called male cone and megasporophyll usually aggregate in a form of female cone in some cases megasporophyll are falling in nature and not aggregated in a form of cones
• the male cone is short life and female cone are long life .female remain in plant until maturity and reaping of seeds.
•microsporophyll contain microsporangia. sporangium contain microspores (distributed by wind always) microspores leavues microsporangia after 3 states normally but it diffeentr in different genes.
On germination
• micropile + Pollen form tube cells. microspores form male gametophyte that is haploid (one or two gametes)
• pollen grains get direct connected with a ovule and deposit on Pollen chamber which after an unfavourable condition germinate here.
• Each Pollen Grain from Pollen tube have two functions
•1-haustorial that used to suck food and 2- sperm career
•That type of structure and functioning of pollen tube is termed as sphonogamic .
•female cone - megasporophyll which contain megasporangia (ovule)
•ovules are orthotropous and unintermic but bitegmic in gnetales
• haploid megaspores developed into female gametophyte which remain surrounded by integumin that is endosperm.
• mature female gametophyte have( two or more or none) archegonia.this phenomena is called polyembryony .
•more then two mature female gametophyte in archigonia called polyembryony.
• each archegonia have single cell ,rentals Canal cell but neck Canal cells are absent .
•male sperm carry to archigonia through Pollen tube( in cycas Pollen tube only used to suck food from endosperm).
• female nuclei and male nuclei combine to form a zygote that is haploid zygote is first cell of sporophytic generation.
The young sporophyte
• zygote developed into embryo
• meroblastic development only Basil part develop to embryo middle and upper part developed into different things
• embryo develop at terminal part of the pressure which pushes the developing embryo into endosperm
•endosperm always haploid in nature because it develop before the fertilization MBA is
•endoscopic that means shoot Apex is directed opposite to micropile.
• the basic characteristic feature of gymnosperm is occurrence of polyembryony but only one embryo develops and mature
• mature embryo differentiated into leaf root stem number of cotyledons in gymnosperms are one two or more
• Cotlyodons are maybe in green in colour while still in close in seeds
• no true fruit are found in gymnosperm.
