TITLE:
Studies on Tracheary Element of Several Native Cycad Species in Australia and Two American Plants
AUTHORS:
Yuyuan Huang, Harvey Ottley, Yolande Yep, Sharon Wilson, David Griffiths, Nikeeta O’sullivan, Yanhua Han, Jane Hempel
KEYWORDS:
Cycad, Evolution, Vessel, Native Species, Structural Characteristics
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.13 No.1,
January
28,
2022
ABSTRACT: Cycas angulata, Cycas armstrongii and Cycas conferta that are native species of Australia
were collected in Darwin city of tropical region, Zamia erosa and angiosperm Guaiacum officinale of
Zygophyllaceae which are introduced collected in the Darwin Botanic Gardens,
and were carried out light microscope and electron microscope observed research
to tracheary element and parenchyma tissue cells of leaflet, rachis and stem.
The results showed that there are more vessel elements in their xylems; the
length of vessel element of Cycadaceae with Zamiaceae are not obvious
difference, the length of vessel element of angiosperm Guaiacum officinale is shorter, but their diameter is smaller, we thought that the characteristics
which the length of vessel element is longer and the diameter is bigger are
more evolutionary, because thus vessel, their number which interconnected
points of possessed perforations’ end walls of vessel element is fewer, and the
passageway space is larger so that the conduction speed and quantity are faster
and more in unit length range and unit time. These vessels are annular vessels,
spiral vessels, scalariform vessels,
reticular vessels, pitted vessels and scalariform-pitted vessels, etc. In the
transverse section, the vessel elements of Cycadaceae and Zamiaceae are
circular, polygonous, more similar to vessel characteristics of leaf and stem of some angiosperms; however, the number of
circular vessel of Guaiacum officinale is
more, about occupy 35%, others are polygonous. The diameter of vessel is that
annular vessel, spiral vessel is least, scalariform
vessel or scalariform-reticular vessel is medium, reticular vessel and pitted vessel are the biggest, the
characteristic is same as angiosperm. In Cycas conferta, etc.
plants often can see several large perforations in the end walls, some species
are several big scalariform or pitted
perforations formed multiple perforation plates, in many vessel element lateral
walls, there are some perforations formed a horizontal transport avenue of
aqueous solution. The scale of diameter of Cycas vessel element is
similar to that of Zamia, but the diameter of more vessel elements of Cycas angulata and Cycas conferta is bigger than the latter, and is bigger
than that of Guaiacum officinale, although Cycas plants
are more primitive than Zamia plants,
and Guaiacum officinale is more evolutionary, but the scale of vessel
diameter of Cycas plants is similar to Zamia or bigger than the latter, even larger than Guaiacum
officinale, these showed that
cycads have evolutionary and more developed characteristics in aqueous
solution transport system. In Guaiacum officinale, more vessel element
has been not seen the ridges in the different directions of side walls which
can make vessel has more mechanical supportability, but some possessed the
ridges; however, more vessel elements are twist shape and can twist together
each other, thus the state can increase their mechanical supportability, and
their synergy with fiber elements which is longer with a twist shape, therefore
their capability of xylem conduction and the combine mechanical support
capability with mechanical tissue are also stronger. In the respect of observed
parenchyma tissue, any parenchyma tissue cells are without perforation, all
cell walls are smoothed and like a membrane. Aimed at only one or two people
pointed the query about Jeffery’s method, some scholars have made comparative
researches, their research used as following methods: 1) The fresh materials
were cut sections 1 - 2 mm thick by hand (the query person provided and thought
right method), were examined with SEM. 2) The materials were treated by
Jeffrey’s Fluid and observed with SEM and so on. The results showed that the
pit membrane, the remnants in the perforation and the structural
characteristics of perforations were not different; and the results of our
comparative research in past time and this research all justified that
Jeffrey’s method is reliable and reasonable. Meanwhile, our research results
showed that only vessel element can form perforation, in other all parenchyma
tissue cells cannot form perforation are also proved that the perforations of
vessel element are naturally inherited character. Analyzed from the structural
characteristics, although they distributed so far apart from each other, they
are a well and unified taxonomy system; we thought that Australia’ most species
or all species of Cycadaceae came from Asia, and it is impossible from Africa,
because the latter only has one more evolutionary species and lack of fossil of
Cycadaceae, these species of Cycadaceae are the descendants of ancestor
species; America possessed more genera of Zamiaceae, this family is mutual with
Africa and Australia, we thought that these genera of Zamiaceae in Australia
and America came from Pangea before continental drift in Jurassic Period, this
family is also maybe one of the proofs to Australia drifted from Pangea to
present position after Jurassic Period. The characteristics of tracheary
element of several different genera of cycads and angiosperm further showed
that more primary species or taxon, their more tissue characteristics are not
also more primary, because of the need to adapt the environment, they are also
constantly evolving. The research is important significant and theory reference
to understand cycads evolutionary aqueous solution transport system, and
understand the ecological adaptation mechanism which why present cycads of 3
families in world major distributed in tropical or subtropical regions, even
many drought and barren areas.