Dear Anee

c3 is moderate plant and C4 is tropical plant.

Thanks

C4 plants are drought resistance and efficient utilization of CO2

Dear Dr. Aneez

I hope you might have got enough information regarding C3 and C4 by now, but still I would like to mention that C3 and C4 are the names derived from the first stable compound synthesized by the plants during CO2 fixation.

In case of C3 plants, CO2 is condensed with RuBP by the help of RuBisCO enzyme to yield first stable product PGA which is a three carbon compound, hence the name C3. On the other hand, in C4 plants, CO2 is entrapped by condensing with PEP, aided by PEPCase enzyme to yield OAA - a four carbon compound which is the first stable product in this case, hence the name C4.

I really don not have any idea about Honey

Best wishes  

In a C3 plant the primary fixation of carbon is catalysed by Rubisco that uses CO2. The first stable compound is a 3 carbon compound and that is why the designation C3. In a C4 plant the primary fixation of carbon is catalysed by PEP carboxylase that uses bicarbonate as substrate. This reaction yields an organic acid with 4 carbons and this is reason for the designation C4. This four carbon organic acid is further decarboxylated releasing CO2 that will enter Calvin cycle through the fixation by Rubisco.  The C4 mechanism allows high concentrations of CO2 next to Rubisco inhibiting the fixation of O2 by Rubisco and the loss of C to photorespiration. Most C4 plants display Kranz anatomy and all display chloroplastic dimorphism where some chloroplasts don’t have functional Rubisco and some others have. Sorry, but I don’t know anything about honey. Hope this has been helpful.

Dear Dr Ahamad,

Your question is interesting but I wonder where the evidence is from that honey can only be based on C3 plant sugars. As others have clearly written, C3 and C4 is a distinction based on photosynthetic biochemistry. The main sugars, and especially sucrose, are  produced in both C3 and C4 and will be identical as far as honey production is concerned. At least that is my assessment - so where is the evidence please?  A more likely scenario is that bees get sugars from flowers with which they have evolved (co-evolution) and so flowers produce sugars (nectar or exudates) as attractants (along with pollen, and colourful petals). Many C4 plants are grasses or similar which are wind pollinated so do not attract bees, How many C4 plants attract bees with nectar? Perhaps there are relatively few and so honey is mainly from C3 plants?  Perhaps the literature contains some answers?  Best wishes

David Lawlor

1. Probably it is not necessary true that honey production requires exlusively C3 plant's sugars (because honey is also produced from CAM plants, see attached example: Cactus honey), but rather, (according to reports) most commercial honey produced by bee are from C3 plants [see attached paper].

2. Due to the expensive of honey (mainly from C3 plants), some impure/adulterated honey were sold by adding sugar cane (C4) or corn syrup (C4). So, a way of detecting pure honey is necessary. ¹³C isotope is used to detect pure honey from adulterated honey. The ratio of  ¹³C detection of adulterated and pure honey will be different. [ http://www.minervascientific.co.uk/index.php?s=services&p=honeyadulteration ]

3. Why are most commercial honey produced by bee from C3 plants? David raised some good points: "propably 'co-evolution' and many C4 plants are grasses or similar which are wind pollinated so do not attract bees."

Honey analysis by HPLC gives glucose and fructose together should be minimum of 60.0 %.  Sucrose should be less than 5.0 %.  Is the ¹³C is indicative of total sugars other than sucrose.  Little confused  Dr.  Yuan-Yeu Yau

Hi Aneez Ahamad,

Please see the attached paper for details of detecting pure honey (mainly from C3 plants) from adulterated honey (adulterated usually with cane sugar or corn syrup, both are C4 plants).

This is one of the paragraphs from this paper:

" The isotopic technique for the detection of adulterated honey is based on the natural differences in isotopic ratios between plants utilising C3 and C4 photosynthetic pathways. Generally, C4 plants, for example, corn, have 13C/12C isotope ratios, referred to as δ13C values, ranging between -8 to -13 ‰, whereas C3 plants, generally nectar-bearing plants, have values between -22 and -30 ‰ ."

Hello,

An interesting discussion. It seems  that the original question was related more to the isotopic differences between sugars from C3 and C4 plants than to the use by bees of different  plant types as sources of sugars.  As has been stated the different mechanisms in C3, C4 and CAM plants result in differences in the proportions of heavy and light carbon isotopes from CO2 being assimilated. So the sugars produced differ - this can be detected and so the source of the sugars can be determined - useful in the case of adulteration of honey made from C3 plants with sugars derived from C4 plants, particularly sugar cane,  I do not know about adulteration with sucrose from sugar beet, which is  C3.  Also, I believe there is no biochemical difference between sucrose from C3 and C4 plants but is there evidence about this?

@ David,

They should have no biochemical difference between sucrose from C3 and C4 plants. One of the differences is, as you said, C3 and C4 plants result in differences in the proportions of heavy and light carbon isotopes from CO2 (atmospheric CO2  contains 1.1% of non-radioactive stable isotope 13C and 98.9% 12C) being assimilated. See the attached classic paper. In the paper, it shows the different ratio of these carbons in C3 and C4 plants. I think it is very interesting.

And I think the original question more focus on why the majority of the honey (produced by bee) come from C3 plants. This phenomenon may give the misconception that honey can only be make from C3 plant sugars.

Regarding sucrose from C3 and C4 plants - they are not identical due to the C-isotope differences. This may not affect much of the biochemistry but could, potentially, affect some processes if, for example, enzyme reactions discriminate.

The original question now seems to have been concerned with the problem of adulteration of honey with cane sugar, with confusion about the sources of sugars used by bees.

1. C3 plants are those where the first product of photosynthesis is a 3 carbon compound i.e. PGA while C4 plants are those where the first product of photosynthesis is a 4 carbon compound i.e. OAA

2. C4 plants are characterized by Kranz anatomy where bundle sheath cells surrounding the vascular bundle contains chloroplasts while C3 plants lack Kranz anatomy.

3. In C4 plants, C3 and C4 cycle are spatially separated i.e. C4 cycle occurs in mesophyll cells while C3 cycle occurs in bundle sheath cells. In C3 plants only C3 cycle occurs in the mesophyll cells.

4. In C3 plants carboxylation reaction is accomplished by the enzyme RUBP carboxylase while in C4 plants the carboxylation reaction is accomplished by the enzyme PEP carboxylase.

5. C4 plants are adapted to warm and dry climates while the C3 plants are adapted to cool and humid climate.

Thanks Arvind for a clear answer

Dear all,

I have a flower honey sample produced under UAE Enviroment t during spring of 2019 this sample has a aC-4 27% while the regulation and the standerizations her should be not more than 7%. Her, there are many wild plants during the shortage spring. What I can do to aviod this limites again next year?@ David W. Lawlor, Arvind Singh